KMail re-downloads POP3 emails that are supposed to be deleted

[Ingo Klöcker]

On Freitag, 11. April 2025 20:14:33 Mitteleuropäische Sommerzeit Kai Bojens 
wrote:
> > Am 11.04.2025 um 20:10 schrieb Jörg Schaible <joerg.schaible at gmx.de>:
> > 
> > Well, since you said you're using POP3, so I ask myself, how can you ever
> > re- download emails? This is not how the POP3 protocol works.
> 
> No, this is exactly how POP3 works.

Yes and no.

> The client can ask the server to delete
> the mails after the download, but it doesn’t have to. You can of course
> download a copy and keep them for a specified time on the server.

The original idea of the POP protocol was to download all emails once and then 
delete them after successful download. For obvious reasons, that's a problem 
if you want to read your email on multiple devices. That's why many email 
clients offer to keep the downloaded mails on the server for some time so that 
the other email clients have a chance to download the emails as well.

This hack, because in my opinion that's what it is, a hack, requires that the 
server provides a unique identifier (UID) for each email that never changes. A 
possible reason for a re-download of emails is that the server for some reason 
changed those unique identifiers. (This brings back memories from decades ago 
when I analyzed such problems.) Another possible reason is that the server 
doesn't remove the messages although KMail asks it to delete them. KMail will 
remove the UIDs from its book-keeping when it thinks that the server has 
deleted them. And then it will redownload them the next time. Without 
inspecting the communication between KMail and the server we won't know if the 
server is the culprit or if there's a regression in KMail.

Running
```
QT_LOGGING_RULES="org.kde.pim.pop3resource.debug=true" akonadictl restart 2>&1 
| grep org.kde.pim.pop3resource  >pop.log
```
in Konsole should write the communication between KMail (or, more precisely, 
the POP3 resource that handles the communication) and the server to the file 
pop.log. WARNING: This file may contain your password in slightly obfuscated 
form. Don't publish this file as-is, but redact anything that looks like 
sensitive information.

The POP3 resource stores the list of UIDs of the downloaded emails and the 
date/time when those emails were downloaded to the config file of the resource 
which should be something like ~/.config/akonadi_pop3_resource_0rc for the first 
configured POP3 account. Compare the list of UIDs stored in the config file with 
the list of UIDs you should find in the pop.log file.

Regards,
Ingo
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