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

HoracioS

Regular Pleskian
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
 
Same issue as reported here:


We've had this issue affect a couple of clients (with the double-whammy of Dovecot crashing from the other issue before that), it's very frustrating.
One wonders if any testing was done at all prior to release...
 
Hello,
We have the same issue and we have find a bypass for UIDL by creating a file : /etc/dovecot/conf.d/99-local-pop3.conf
With :
protocol pop3 {
# UIDL stable recommandé (évite les re-téléchargements)
pop3_uidl_format = %{uid | hex(8)}%{uidvalidity | hex(8)}

# Optionnels mais utiles :
# Réutiliser un éventuel X-UIDL déjà présent dans les entêtes
# pop3_reuse_xuidl = yes
# En cas d’UIDL dupliqués, renommer plutôt qu’échouer
# pop3_uidl_duplicates = rename
}

We have a question : the next update 18.0.73 Update 1 will make an issue with our bypass?
 
@CMRP The update should not override the file /etc/dovecot/conf.d/99-local-pop3.conf, thus, your customization should remain intact. However, if I am not mistaken, your custom config will be enforced over Plesk's config, and I cannot confirm for sure whether that won't create issues in the future.
 
Thank you for your response.

We know that is not the normal way but, many customers had a lot of trouble with the new update and cannot wait for an update that will arrive in several days.
 
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