Issue After upgrading to 18.0.73: POP3 re-download storm due to index/UID changes (Dovecot 2.4.1)

[HoracioS]

Server operating system version

Debian 11.11

Plesk version and microupdate number

18.0.73

After updating to 18.0.73, POP3 accounts begin re-downloading all messages. Server logs show index rebuilds / changes around the upgrade window. POP3 clients treat every message as new.

What seems to be happening (technical)

• The current pop3_uidl_format uses %{uid} and ${uidvalidity}.
• If uidvalidity changes and/or indexes/uidlists are rebuilt, the server publishes different UIDLs.
• POP3 clients rely on stable UIDL; when UIDL changes, they re-fetch everything by design.

How to confirm

1. Check current Dovecot + config:
   
   dovecot --version
   doveconf -n | egrep -i 'pop3_|uidl|uidvalidity|mail_location'
   
   
2. Inspect mailbox UIDVALIDITY:
   
   doveadm mailbox status -u user@domain INBOX uidvalidity
   
   
3. Check if indexes were recreated around the upgrade:
   
   ls -l --time=ctime /var/qmail/mailnames/<domain>/<user>/Maildir/ | egrep 'dovecot\.(index|uidlist)'

Impact

• POP3 users re-download entire mailboxes (duplicates locally if clients don’t de-dupe).
• Bandwidth/storage spikes; support load increases.

I’m going to suspend Plesk updates because users are furious — and with good reason. Couldn’t Plesk have anticipated this problem beforehand?

Best regards,
Horacio Stolovitzky