fix(pop3): batch delete in one session

[FromSi]

What?

POP3 batch deletion now sends requests like this:

CONNECT
AUTH
UIDL
DELE 1
DELE 2
DELE 3
QUIT

QUIT is sent once at the end, so all DELE commands are committed in one POP3 session.

Why?

Closes #555

Previously, batch deletion sent requests like this:

CONNECT
AUTH
UIDL
DELE 1
QUIT

CONNECT
AUTH
UIDL
DELE 2
QUIT

CONNECT
AUTH
UIDL
DELE 3
QUIT

So deleting multiple emails repeated the full connection/authentication cycle for every message.

[FromSi]

@andrinoff

One related thing I noticed while testing locally: I could not get messages to load through the POP3 backend path itself. Messages only appeared for me when the account config also had IMAP settings with "service_provider": "custom".

That creates a mismatch for this case: the message IDs shown in the UI come from IMAP, but batch deletion is then executed through the POP3 provider. POP3 maps messages by hashed UIDL values, so the IMAP UIDs do not match the POP3 UID lookup and batch deletion can fail with pop3: message with UID ... not found.

This might be an issue with my local setup/configuration, but I think it would be good for someone else to verify this case with a real POP3 account.

[andrinoff]

I'll check it out, thank you, @FromSi

[andrinoff]

i will check out the behaivor you commented on a bit later, this is the only issue i see with this PR

fixed.

[andrinoff]

@FromSi make your membership to the org public, please. Also, if you can -- join the Discord, so that it is easier to talk to you.