发信改为事务内每 300 人分批写入，避免全校群发一次插入过大；数据库异常现在返回明确的 503，不再只显示模糊 500。

校级、学院级管理员支持按学院、身份、行政班、教学班、姓名/学号/工号筛选，也可指定最多 500 名收件人。所有结果均由服务端重新校验权限。
接入 CKEditor 5，支持标题、列表、引用和链接；正文扩展为 MySQL longtext。
富文本在收件箱、详情弹窗和已发送记录中统一经 DOMPurify 净化后展示。
页面改用系统现有的冷白、靛蓝、青绿色令牌，新增“选择收件人 → 编辑内容”工作台和移动端适配。

src/Jiaowu.Api/Controllers/NotificationsController.cs

@@ -1,4 +1,7 @@
 using System.ComponentModel.DataAnnotations;
+using System.Data;
+using System.Net;
+using System.Text.RegularExpressions;
 using Jiaowu.Api.Domain.Academic;
 using Jiaowu.Api.Domain.Identity;
 using Jiaowu.Api.Infrastructure.Auth;
@@ -14,8 +17,11 @@ namespace Jiaowu.Api.Controllers;
 [Route("api/notifications")]
 public sealed class NotificationsController(
     AppDbContext db,
-    ICurrentUserDataScope currentUserDataScope) : ControllerBase
+    ICurrentUserDataScope currentUserDataScope,
+    ILogger<NotificationsController>? logger = null) : ControllerBase
 {
+    private const int MaximumSelectedRecipients = 500;
+    private const int NotificationBatchSize = 300;
     private const string Senders =
         SystemRoles.SuperAdmin + "," +
         SystemRoles.AcademicAdmin + "," +
@@ -106,17 +112,12 @@ public sealed class NotificationsController(
         var scope = currentUserDataScope.Current;
         if (IsSchoolAdministrator(scope))
         {
-            var recipientCount = await db.Users.AsNoTracking()
+            return Ok(await BuildAdministratorComposerAsync(
-                .CountAsync(
+                scope,
-                    x => x.IsEnabled && x.Id != scope.UserId,
+                null,
-                    cancellationToken);
+                MessageAudienceType.School,
-            return Ok(new
+                "全校已启用账号",
-            {
+                cancellationToken));
-                AudienceType = MessageAudienceType.School,
-                AudienceName = "全校已启用账号",
-                RecipientCount = recipientCount,
-                TeachingTasks = Array.Empty<object>()
-            });
         }
 
         if (scope.IsInRole(SystemRoles.CollegeAdmin) ||
@@ -138,19 +139,12 @@ public sealed class NotificationsController(
             if (college is null)
                 return ConflictProblem("当前账号关联的学院不存在。");
 
-            var recipientCount = await db.Users.AsNoTracking()
+            return Ok(await BuildAdministratorComposerAsync(
-                .CountAsync(
+                scope,
-                    x => x.IsEnabled &&
+                collegeId.Value,
-                         x.Id != scope.UserId &&
+                MessageAudienceType.College,
-                         x.CollegeId == collegeId.Value,
+                $"{college}全院成员",
-                    cancellationToken);
+                cancellationToken));
-            return Ok(new
-            {
-                AudienceType = MessageAudienceType.College,
-                AudienceName = $"{college}全院成员",
-                RecipientCount = recipientCount,
-                TeachingTasks = Array.Empty<object>()
-            });
         }
 
         if (scope.IsInRole(SystemRoles.Teacher))
@@ -195,6 +189,114 @@ public sealed class NotificationsController(
         return Forbid();
     }
 
+    [HttpGet("recipients")]
+    [Authorize(Roles = Senders)]
+    public async Task<ActionResult> GetRecipients(
+        Guid? collegeId,
+        string? role,
+        Guid? administrativeClassId,
+        Guid? teachingTaskId,
+        string? keyword,
+        int page = 1,
+        int pageSize = 30,
+        CancellationToken cancellationToken = default)
+    {
+        var scope = currentUserDataScope.Current;
+        if (scope.IsInRole(SystemRoles.Teacher) &&
+            !IsSchoolAdministrator(scope) &&
+            !scope.IsInRole(SystemRoles.CollegeAdmin) &&
+            !scope.IsInRole(SystemRoles.Counselor))
+        {
+            return Forbid();
+        }
+
+        var resolvedCollegeId = IsSchoolAdministrator(scope)
+            ? null
+            : await ResolveSenderCollegeIdAsync(scope, cancellationToken);
+        if (!IsSchoolAdministrator(scope) && !resolvedCollegeId.HasValue)
+            return ConflictProblem("当前账号未关联学院，暂时无法确定收件人范围。");
+
+        var filter = new MessageRecipientFilter(
+            collegeId,
+            Normalize(role),
+            administrativeClassId,
+            teachingTaskId,
+            Normalize(keyword));
+        if (filter.Role is not null && !SystemRoles.All.Contains(filter.Role))
+            return ValidationProblem("所选身份类型无效。");
+
+        page = Math.Max(1, page);
+        pageSize = Math.Clamp(pageSize, 10, 100);
+        var source = ApplyRecipientFilter(
+            ScopedRecipientQuery(scope, resolvedCollegeId),
+            filter);
+        var total = await source.CountAsync(cancellationToken);
+        var users = await source
+            .OrderBy(x => x.DisplayName)
+            .ThenBy(x => x.UserName)
+            .Skip((page - 1) * pageSize)
+            .Take(pageSize)
+            .Select(user => new
+            {
+                user.Id,
+                user.DisplayName,
+                user.UserName,
+                user.StaffNumber,
+                CollegeName = db.Colleges
+                    .Where(college => college.Id == user.CollegeId)
+                    .Select(college => college.Name)
+                    .FirstOrDefault(),
+                StudentNumber = db.Students
+                    .Where(student => student.UserId == user.Id)
+                    .Select(student => student.StudentNumber)
+                    .FirstOrDefault(),
+                ClassName = db.Students
+                    .Where(student => student.UserId == user.Id)
+                    .Select(student => student.AdministrativeClass!.Name)
+                    .FirstOrDefault(),
+                TeacherNumber = db.Teachers
+                    .Where(teacher => teacher.UserId == user.Id)
+                    .Select(teacher => teacher.TeacherNumber)
+                    .FirstOrDefault()
+            })
+            .ToListAsync(cancellationToken);
+        var userIds = users.Select(x => x.Id).ToArray();
+        var roleRows = await db.UserRoles.AsNoTracking()
+            .Where(x => userIds.Contains(x.UserId))
+            .Join(
+                db.Roles.AsNoTracking(),
+                userRole => userRole.RoleId,
+                roleEntity => roleEntity.Id,
+                (userRole, roleEntity) => new
+                {
+                    userRole.UserId,
+                    RoleName = roleEntity.Name!
+                })
+            .ToListAsync(cancellationToken);
+        var rolesByUser = roleRows
+            .GroupBy(x => x.UserId)
+            .ToDictionary(
+                group => group.Key,
+                group => group.Select(x => x.RoleName).Distinct().ToArray());
+
+        return Ok(new
+        {
+            Items = users.Select(user => new
+            {
+                user.Id,
+                user.DisplayName,
+                user.UserName,
+                Number = user.StudentNumber ?? user.TeacherNumber ?? user.StaffNumber,
+                user.CollegeName,
+                user.ClassName,
+                Roles = rolesByUser.GetValueOrDefault(user.Id, [])
+            }),
+            Total = total,
+            Page = page,
+            PageSize = pageSize
+        });
+    }
+
     [HttpPost("send")]
     [Authorize(Roles = Senders)]
     public async Task<ActionResult> Send(
@@ -205,8 +307,10 @@ public sealed class NotificationsController(
         var content = request.Content.Trim();
         if (title.Length == 0)
             return ValidationProblem("请填写消息标题。");
-        if (content.Length == 0)
+        if (PlainText(content).Length == 0)
             return ValidationProblem("请填写消息正文。");
+        if (content.Length > 20000)
+            return ValidationProblem("消息正文过长，请精简至 20000 个字符以内。");
         var scope = currentUserDataScope.Current;
         MessageAudienceType audienceType;
         Guid? audienceId = null;
@@ -215,12 +319,16 @@ public sealed class NotificationsController(
 
         if (IsSchoolAdministrator(scope))
         {
-            audienceType = MessageAudienceType.School;
+            var result = await ResolveAdministratorRecipientsAsync(
-            audienceName = "全校已启用账号";
+                scope,
-            recipientIds = await db.Users.AsNoTracking()
+                null,
-                .Where(x => x.IsEnabled && x.Id != scope.UserId)
+                request,
-                .Select(x => x.Id)
+                "全校已启用账号",
-                .ToListAsync(cancellationToken);
+                cancellationToken);
+            if (result.Error is not null) return result.Error;
+            audienceType = result.AudienceType;
+            audienceName = result.AudienceName!;
+            recipientIds = result.RecipientIds!;
         }
         else if (scope.IsInRole(SystemRoles.CollegeAdmin) ||
                  scope.IsInRole(SystemRoles.Counselor))
@@ -241,16 +349,19 @@ public sealed class NotificationsController(
             if (collegeName is null)
                 return ConflictProblem("当前账号关联的学院不存在。");
 
-            audienceType = MessageAudienceType.College;
+            var result = await ResolveAdministratorRecipientsAsync(
-            audienceId = collegeId.Value;
+                scope,
-            audienceName = $"{collegeName}全院成员";
+                collegeId.Value,
-            recipientIds = await db.Users.AsNoTracking()
+                request,
-                .Where(x =>
+                $"{collegeName}全院成员",
-                    x.IsEnabled &&
+                cancellationToken);
-                    x.Id != scope.UserId &&
+            if (result.Error is not null) return result.Error;
-                    x.CollegeId == collegeId.Value)
+            audienceType = result.AudienceType;
-                .Select(x => x.Id)
+            audienceId = audienceType == MessageAudienceType.College
-                .ToListAsync(cancellationToken);
+                ? collegeId.Value
+                : null;
+            audienceName = result.AudienceName!;
+            recipientIds = result.RecipientIds!;
         }
         else if (scope.IsInRole(SystemRoles.Teacher))
         {
@@ -305,24 +416,54 @@ public sealed class NotificationsController(
             RecipientCount = recipientIds.Count,
             LinkUrl = null
         };
-        dispatch.Notifications = recipientIds.Select(userId => new Notification
+        try
         {
-            UserId = userId,
+            return await db.ExecuteInRetriableTransactionAsync<ActionResult>(
-            Title = title,
+                async transaction =>
-            Content = content,
+                {
-            Category = NotificationCategory.General,
+                    db.MessageDispatches.Add(dispatch);
-            LinkUrl = null
+                    await db.SaveChangesAsync(cancellationToken);
-        }).ToList();
+                    db.ChangeTracker.Clear();
 
-        db.MessageDispatches.Add(dispatch);
+                    foreach (var batch in recipientIds.Chunk(NotificationBatchSize))
-        await db.SaveChangesAsync(cancellationToken);
+                    {
-        return Ok(new
+                        db.Notifications.AddRange(batch.Select(userId => new Notification
+                        {
+                            UserId = userId,
+                            Title = title,
+                            Content = content,
+                            Category = NotificationCategory.General,
+                            LinkUrl = null,
+                            MessageDispatchId = dispatch.Id
+                        }));
+                        await db.SaveChangesAsync(cancellationToken);
+                        db.ChangeTracker.Clear();
+                    }
+
+                    await transaction.CommitAsync(cancellationToken);
+                    return Ok(new
+                    {
+                        dispatch.Id,
+                        dispatch.AudienceName,
+                        dispatch.RecipientCount,
+                        dispatch.CreatedAt
+                    });
+                },
+                cancellationToken,
+                IsolationLevel.ReadCommitted);
+        }
+        catch (DbUpdateException exception)
         {
-            dispatch.Id,
+            logger?.LogError(
-            dispatch.AudienceName,
+                exception,
-            dispatch.RecipientCount,
+                "Failed to send notification dispatch {DispatchId} to {RecipientCount} recipients.",
-            dispatch.CreatedAt
+                dispatch.Id,
-        });
+                recipientIds.Count);
+            return Problem(
+                title: "消息未能发送",
+                detail: "消息数据保存失败。请确认数据库已完成最新升级后重试；本次消息没有发送。",
+                statusCode: StatusCodes.Status503ServiceUnavailable);
+        }
     }
 
     [HttpGet("sent")]
@@ -433,6 +574,286 @@ public sealed class NotificationsController(
         scope.IsInRole(SystemRoles.SuperAdmin) ||
         scope.IsInRole(SystemRoles.AcademicAdmin);
 
+    private async Task<object> BuildAdministratorComposerAsync(
+        CurrentUserScope scope,
+        Guid? fixedCollegeId,
+        MessageAudienceType audienceType,
+        string audienceName,
+        CancellationToken cancellationToken)
+    {
+        var colleges = await db.Colleges.AsNoTracking()
+            .Where(x => !fixedCollegeId.HasValue || x.Id == fixedCollegeId.Value)
+            .OrderBy(x => x.Code)
+            .Select(x => new { x.Id, x.Code, x.Name })
+            .ToListAsync(cancellationToken);
+        var administrativeClasses = await db.AdministrativeClasses.AsNoTracking()
+            .Where(x =>
+                x.IsEnabled &&
+                (!fixedCollegeId.HasValue ||
+                 x.Major!.CollegeId == fixedCollegeId.Value))
+            .OrderByDescending(x => x.Grade)
+            .ThenBy(x => x.Code)
+            .Select(x => new
+            {
+                x.Id,
+                x.Code,
+                x.Name,
+                x.Grade,
+                CollegeId = x.Major!.CollegeId
+            })
+            .ToListAsync(cancellationToken);
+        var teachingTasks = await db.TeachingTasks.AsNoTracking()
+            .Where(x =>
+                x.Status != TeachingTaskStatus.Draft &&
+                (!fixedCollegeId.HasValue ||
+                 x.Course!.CollegeId == fixedCollegeId.Value))
+            .OrderByDescending(x => x.AcademicTerm!.IsCurrent)
+            .ThenByDescending(x => x.AcademicTerm!.StartDate)
+            .ThenBy(x => x.TaskNumber)
+            .Select(x => new
+            {
+                x.Id,
+                x.TaskNumber,
+                CourseName = x.Course!.Name,
+                TermName = x.AcademicTerm!.Name,
+                CollegeId = x.Course.CollegeId
+            })
+            .ToListAsync(cancellationToken);
+        var recipientCount = await ScopedRecipientQuery(scope, fixedCollegeId)
+            .CountAsync(cancellationToken);
+
+        return new
+        {
+            AudienceType = audienceType,
+            AudienceName = audienceName,
+            RecipientCount = recipientCount,
+            CanFilterRecipients = true,
+            MaximumSelectedRecipients,
+            Colleges = colleges,
+            Roles = RoleOptions,
+            AdministrativeClasses = administrativeClasses,
+            TeachingTasks = teachingTasks
+        };
+    }
+
+    private IQueryable<ApplicationUser> ScopedRecipientQuery(
+        CurrentUserScope scope,
+        Guid? fixedCollegeId)
+    {
+        var source = db.Users.AsNoTracking()
+            .Where(x => x.IsEnabled && x.Id != scope.UserId);
+        if (IsSchoolAdministrator(scope)) return source;
+        if (!fixedCollegeId.HasValue) return source.Where(_ => false);
+        var collegeId = fixedCollegeId.Value;
+        return source.Where(user =>
+            user.CollegeId == collegeId ||
+            db.Students.Any(student =>
+                student.UserId == user.Id &&
+                student.AdministrativeClass!.Major!.CollegeId == collegeId) ||
+            db.Teachers.Any(teacher =>
+                teacher.UserId == user.Id &&
+                teacher.CollegeId == collegeId));
+    }
+
+    private IQueryable<ApplicationUser> ApplyRecipientFilter(
+        IQueryable<ApplicationUser> source,
+        MessageRecipientFilter? filter)
+    {
+        if (filter is null) return source;
+        if (filter.CollegeId.HasValue)
+        {
+            var collegeId = filter.CollegeId.Value;
+            source = source.Where(user =>
+                user.CollegeId == collegeId ||
+                db.Students.Any(student =>
+                    student.UserId == user.Id &&
+                    student.AdministrativeClass!.Major!.CollegeId == collegeId) ||
+                db.Teachers.Any(teacher =>
+                    teacher.UserId == user.Id &&
+                    teacher.CollegeId == collegeId));
+        }
+        if (!string.IsNullOrWhiteSpace(filter.Role))
+        {
+            var role = filter.Role;
+            source = source.Where(user =>
+                db.UserRoles.Any(userRole =>
+                    userRole.UserId == user.Id &&
+                    db.Roles.Any(roleEntity =>
+                        roleEntity.Id == userRole.RoleId &&
+                        roleEntity.Name == role)));
+        }
+        if (filter.AdministrativeClassId.HasValue)
+        {
+            var classId = filter.AdministrativeClassId.Value;
+            source = source.Where(user =>
+                db.Students.Any(student =>
+                    student.UserId == user.Id &&
+                    student.AdministrativeClassId == classId));
+        }
+        if (filter.TeachingTaskId.HasValue)
+        {
+            var taskId = filter.TeachingTaskId.Value;
+            source = source.Where(user =>
+                db.Students.Any(student =>
+                    student.UserId == user.Id &&
+                    (db.TeachingTaskClasses.Any(item =>
+                         item.TeachingTaskId == taskId &&
+                         item.AdministrativeClassId ==
+                         student.AdministrativeClassId) ||
+                     db.CourseEnrollments.Any(enrollment =>
+                         enrollment.StudentId == student.Id &&
+                         enrollment.Status == CourseEnrollmentStatus.Enrolled &&
+                         enrollment.CourseSelectionOffering!.TeachingTaskId ==
+                         taskId))));
+        }
+        if (!string.IsNullOrWhiteSpace(filter.Keyword))
+        {
+            var keyword = filter.Keyword;
+            source = source.Where(user =>
+                user.DisplayName.Contains(keyword) ||
+                (user.UserName != null && user.UserName.Contains(keyword)) ||
+                (user.StaffNumber != null && user.StaffNumber.Contains(keyword)) ||
+                db.Students.Any(student =>
+                    student.UserId == user.Id &&
+                    (student.Name.Contains(keyword) ||
+                     student.StudentNumber.Contains(keyword))) ||
+                db.Teachers.Any(teacher =>
+                    teacher.UserId == user.Id &&
+                    (teacher.Name.Contains(keyword) ||
+                     teacher.TeacherNumber.Contains(keyword))));
+        }
+
+        return source;
+    }
+
+    private async Task<RecipientResolution> ResolveAdministratorRecipientsAsync(
+        CurrentUserScope scope,
+        Guid? fixedCollegeId,
+        SendMessageRequest request,
+        string defaultAudienceName,
+        CancellationToken cancellationToken)
+    {
+        var source = ScopedRecipientQuery(scope, fixedCollegeId);
+        if (request.RecipientMode == MessageRecipientMode.Scope)
+        {
+            return new RecipientResolution(
+                fixedCollegeId.HasValue
+                    ? MessageAudienceType.College
+                    : MessageAudienceType.School,
+                defaultAudienceName,
+                await source.Select(x => x.Id).ToListAsync(cancellationToken),
+                null);
+        }
+
+        if (request.RecipientMode == MessageRecipientMode.Filtered)
+        {
+            if (request.RecipientFilter?.Role is not null &&
+                !SystemRoles.All.Contains(request.RecipientFilter.Role))
+            {
+                return new RecipientResolution(
+                    default,
+                    null,
+                    null,
+                    ValidationProblem("所选身份类型无效。"));
+            }
+            var recipientIds = await ApplyRecipientFilter(
+                    source,
+                    request.RecipientFilter)
+                .Select(x => x.Id)
+                .ToListAsync(cancellationToken);
+            return new RecipientResolution(
+                MessageAudienceType.Custom,
+                BuildFilteredAudienceName(request.RecipientFilter),
+                recipientIds,
+                null);
+        }
+
+        if (request.RecipientMode == MessageRecipientMode.Selected)
+        {
+            var requestedIds = request.RecipientUserIds?
+                .Distinct()
+                .ToArray() ?? [];
+            if (requestedIds.Length == 0)
+            {
+                return new RecipientResolution(
+                    default,
+                    null,
+                    null,
+                    ValidationProblem("请至少选择一名收件人。"));
+            }
+            if (requestedIds.Length > MaximumSelectedRecipients)
+            {
+                return new RecipientResolution(
+                    default,
+                    null,
+                    null,
+                    ValidationProblem(
+                        $"单次最多指定 {MaximumSelectedRecipients} 名收件人。"));
+            }
+
+            var authorizedIds = await source
+                .Where(x => requestedIds.Contains(x.Id))
+                .Select(x => x.Id)
+                .ToListAsync(cancellationToken);
+            if (authorizedIds.Count != requestedIds.Length)
+            {
+                return new RecipientResolution(
+                    default,
+                    null,
+                    null,
+                    ValidationProblem("所选收件人包含无权限访问或已停用的账号。"));
+            }
+
+            return new RecipientResolution(
+                MessageAudienceType.Custom,
+                $"指定收件人（{authorizedIds.Count} 人）",
+                authorizedIds,
+                null);
+        }
+
+        return new RecipientResolution(
+            default,
+            null,
+            null,
+            ValidationProblem("请选择有效的收件方式。"));
+    }
+
+    private static string BuildFilteredAudienceName(MessageRecipientFilter? filter)
+    {
+        if (filter is null) return "当前权限范围内全部账号";
+        var parts = new List<string>();
+        if (filter.CollegeId.HasValue) parts.Add("指定学院");
+        if (filter.Role is not null)
+            parts.Add(RoleOptions.FirstOrDefault(x => x.Value == filter.Role)?.Label ??
+                      filter.Role);
+        if (filter.AdministrativeClassId.HasValue) parts.Add("指定行政班");
+        if (filter.TeachingTaskId.HasValue) parts.Add("指定教学班");
+        if (filter.Keyword is not null) parts.Add($"关键词“{filter.Keyword}”");
+        return parts.Count == 0
+            ? "当前权限范围内全部账号"
+            : string.Join(" · ", parts);
+    }
+
+    private static string PlainText(string html)
+    {
+        var withoutTags = Regex.Replace(html, "<[^>]+>", " ");
+        return WebUtility.HtmlDecode(withoutTags).Trim();
+    }
+
+    private static string? Normalize(string? value) =>
+        string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+
+    private static readonly RoleOption[] RoleOptions =
+    [
+        new(SystemRoles.Student, "学生"),
+        new(SystemRoles.Teacher, "任课教师"),
+        new(SystemRoles.Counselor, "辅导员"),
+        new(SystemRoles.CollegeAdmin, "学院管理员"),
+        new(SystemRoles.AcademicAdmin, "校级教务管理员"),
+        new(SystemRoles.Leader, "校领导"),
+        new(SystemRoles.SuperAdmin, "超级管理员")
+    ];
+
     private ActionResult ConflictProblem(string detail) =>
         Conflict(new ProblemDetails
         {
@@ -452,8 +873,33 @@ public sealed class NotificationsController(
 
 public sealed record SendMessageRequest(
     [property: Required, StringLength(200)] string Title,
-    [property: Required, StringLength(1000)] string Content,
+    [property: Required, StringLength(20000)] string Content,
-    Guid? TeachingTaskId = null);
+    Guid? TeachingTaskId = null,
+    MessageRecipientMode RecipientMode = MessageRecipientMode.Scope,
+    MessageRecipientFilter? RecipientFilter = null,
+    IReadOnlyCollection<Guid>? RecipientUserIds = null);
+
+public sealed record MessageRecipientFilter(
+    Guid? CollegeId = null,
+    string? Role = null,
+    Guid? AdministrativeClassId = null,
+    Guid? TeachingTaskId = null,
+    string? Keyword = null);
+
+public enum MessageRecipientMode
+{
+    Scope = 1,
+    Filtered = 2,
+    Selected = 3
+}
+
+public sealed record RoleOption(string Value, string Label);
+
+internal sealed record RecipientResolution(
+    MessageAudienceType AudienceType,
+    string? AudienceName,
+    List<Guid>? RecipientIds,
+    ActionResult? Error);
 
 /// <summary>
 /// Centralized helper to send notifications across the app.

src/Jiaowu.Api/Domain/Academic/NotificationEntities.cs

@@ -44,5 +44,6 @@ public enum MessageAudienceType
 {
     School = 1,
     College = 2,
-    TeachingTask = 3
+    TeachingTask = 3,
+    Custom = 4
 }

src/Jiaowu.Api/Infrastructure/Persistence/AppDbContext.cs

@@ -980,7 +980,7 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         builder.Entity<Notification>(entity =>
         {
             entity.Property(x => x.Title).HasMaxLength(200);
-            entity.Property(x => x.Content).HasMaxLength(1000);
+            entity.Property(x => x.Content).HasColumnType("longtext");
             entity.Property(x => x.LinkUrl).HasMaxLength(300);
             entity.HasIndex(x => new { x.UserId, x.IsRead });
             entity.HasIndex(x => new { x.UserId, x.Category, x.CreatedAt });
@@ -996,7 +996,7 @@ public sealed class AppDbContext(DbContextOptions<AppDbContext> options)
         {
             entity.Property(x => x.SenderName).HasMaxLength(100);
             entity.Property(x => x.Title).HasMaxLength(200);
-            entity.Property(x => x.Content).HasMaxLength(1000);
+            entity.Property(x => x.Content).HasColumnType("longtext");
             entity.Property(x => x.AudienceName).HasMaxLength(200);
             entity.Property(x => x.LinkUrl).HasMaxLength(300);
             entity.HasIndex(x => new { x.SenderUserId, x.CreatedAt });