Receive Repeated Email When Using Email Client

Diagnose and fix duplicate emails when retrieving Alibaba Mail with a POP3 email client.

Description

Emails are received repeatedly when using an email client to retrieve mail from Alibaba Mail.

Cause

• The sender's third-party email client exited abnormally—for example, due to a crash or forced close—without issuing a QUIT command. The POP3 QUIT command moves the session from the transaction state to the update state, telling the server to mark downloaded messages as retrieved. Without QUIT, the server treats the session as incomplete and re-delivers those messages on the next connection.

• The network connection is poor or unstable. A dropped connection during a POP3 session can prevent the QUIT command from reaching the server, causing the server to re-deliver the same messages on the next connection.

• Antivirus or email monitoring software intercepts the email client's POP3 connection and re-transmits each message through its own send/receive cycle. Every message is then processed twice—once by the monitoring software and once by the email client—resulting in duplicates.

• A POP3 email proxy is configured in Alibaba Mail Webmail. The system automatically collects external email each time you log in to Webmail. If you also retrieve that same external account with a POP3 client, the same messages are downloaded twice—once by Webmail and once by the client. Unlike the other causes, this problem occurs on every new Webmail login rather than intermittently.

Solution

• Contact the sender and ask them to restart their third-party email client so the POP3 session ends cleanly.

• Run the following tracert command to check network quality. Wait for a stable connection before retrieving email.

  tracert [$Domain]

  Note

  Replace [$Domain] with your Alibaba Mail domain name.

• Restart the email monitoring software. If duplicates persist, temporarily disable it to confirm whether it is the source of the problem.

• Turn off the "delete from server after download" setting in your email client. This keeps messages on the server so both Webmail and the client can access them without re-downloading. Alternatively, switch to IMAP instead of POP3. IMAP synchronizes state across all clients, eliminating the class of duplication problems caused by POP3 session management.

How POP3 works

The POP3 protocol uses three session states defined in RFC 1939:

1. Authorization state: The client connects and authenticates with the server.

2. Transaction state: The client retrieves, lists, or deletes messages.

3. Update state: The client sends the QUIT command, which causes the server to apply pending deletions and close the session.

If a session ends without QUIT, the server does not enter the update state and treats all downloaded messages as unread on the next connection.

Applicable scope

• Alibaba Mail