diff --git a/src/messages/messages.gateway.ts b/src/messages/messages.gateway.ts
index a236fed..d5fdf93 100644
--- a/src/messages/messages.gateway.ts
+++ b/src/messages/messages.gateway.ts
@@ -99,6 +99,26 @@ export class MessagesGateway implements OnGatewayConnection, OnGatewayDisconnect
       .catch((err) => {
         this.logger.warn(`Failed to update online status for ${userId}: ${err.message}`);
       });
+
+    // Mark pending SENT messages as DELIVERED now that this user is online
+    this.messagesService.markPendingMessagesAsDelivered(userId)
+      .then((results) => {
+        for (const result of results) {
+          // Notify each sender that their messages were delivered
+          const deliveredEvent = {
+            messageIds: result.messageIds,
+            conversationId: result.conversationId,
+            deliveredAt: result.deliveredAt,
+          };
+          this.sendToUser(result.senderId, 'message_delivered', deliveredEvent);
+        }
+        if (results.length > 0) {
+          this.logger.log(`Marked pending messages as delivered for ${userId} across ${results.length} conversation(s)`);
+        }
+      })
+      .catch((err) => {
+        this.logger.warn(`Failed to mark pending messages as delivered for ${userId}: ${err.message}`);
+      });
   }
 
   /**
@@ -190,6 +210,18 @@ export class MessagesGateway implements OnGatewayConnection, OnGatewayDisconnect
             ? participants.agentUserId
             : participants.userId;
           this.sendToUser(otherUserId, 'new_message', message);
+
+          // Auto-mark as DELIVERED if recipient is online
+          if (this.isUserOnline(otherUserId)) {
+            await this.messagesService.markMessageDelivered(message.id);
+            const deliveredEvent = {
+              messageId: message.id,
+              conversationId: data.conversationId,
+              deliveredAt: new Date(),
+            };
+            // Notify sender that message was delivered
+            this.sendToUser(client.userId, 'message_delivered', deliveredEvent);
+          }
         }
       } catch (participantError) {
         this.logger.warn(`Failed to get participants for direct delivery in ${data.conversationId}: ${participantError.message}`);
diff --git a/src/messages/messages.service.ts b/src/messages/messages.service.ts
index aacbbc4..79a0a59 100644
--- a/src/messages/messages.service.ts
+++ b/src/messages/messages.service.ts
@@ -528,6 +528,52 @@ export class MessagesService {
     });
   }
 
+  /**
+   * Mark all SENT messages addressed to a user as DELIVERED (when they come online)
+   * Returns the updated messages grouped by conversation for notification purposes
+   */
+  async markPendingMessagesAsDelivered(userId: string): Promise<{ conversationId: string; senderId: string; messageIds: string[]; deliveredAt: Date }[]> {
+    const now = new Date();
+
+    // Find all conversations where this user is a participant
+    const conversations = await this.prisma.conversation.findMany({
+      where: {
+        OR: [
+          { userId },
+          { agentProfile: { userId } },
+        ],
+      },
+      select: { id: true, userId: true, agentProfile: { select: { userId: true } } },
+    });
+
+    const results: { conversationId: string; senderId: string; messageIds: string[]; deliveredAt: Date }[] = [];
+
+    for (const conv of conversations) {
+      const otherUserId = conv.userId === userId ? conv.agentProfile.userId : conv.userId;
+
+      // Find SENT messages from the other user in this conversation
+      const sentMessages = await this.prisma.message.findMany({
+        where: {
+          conversationId: conv.id,
+          senderId: otherUserId,
+          status: MessageStatus.SENT,
+        },
+        select: { id: true },
+      });
+
+      if (sentMessages.length > 0) {
+        const messageIds = sentMessages.map((m) => m.id);
+        await this.prisma.message.updateMany({
+          where: { id: { in: messageIds } },
+          data: { status: MessageStatus.DELIVERED, deliveredAt: now },
+        });
+        results.push({ conversationId: conv.id, senderId: otherUserId, messageIds, deliveredAt: now });
+      }
+    }
+
+    return results;
+  }
+
   /**
    * Get conversation by ID with full details
    */