UID validity is changed

[link2xt]

On Jul 13 many user accounts got new INBOX UID validity resulting in lost messages due to deltachat/deltachat-core-rust#5774

We use maildir format.

User home contains files dovecot-uidlist and dovecot-uidvalidity.
dovecot-uidvalidity is created by mailbox_uidvalidity_write here:
https://github.com/dovecot/core/blob/52c9f93b1d9a343374f7b586a365d47dbed40bf4/src/lib-storage/mailbox-uidvalidity.c#L69
It contains UID validity as a hex value.
For example:

# cat dovecot-uidvalidity
6690a34c

0x6690a34c is 1720755020

The same UID validity is stored in dovecot-uidlist as the first entry:

# head -1 dovecot-uidlist
3 V1720755020 N1 G...

V corresponds to UID validity:
https://github.com/dovecot/core/blob/52c9f93b1d9a343374f7b586a365d47dbed40bf4/src/lib-storage/index/maildir/maildir-uidlist.h#L33

This is probably caused by cronjob removing files directly from the maildir and somehow causes Dovecot to recreate dovecot-uidlist. Affected users have dovecot-uidlist recreated with mtime and UID validity corresponding to Jul 13.

Some documentation of uidlist is at the beginning of maildir-sync:
https://github.com/dovecot/core/blob/52c9f93b1d9a343374f7b586a365d47dbed40bf4/src/lib-storage/index/maildir/maildir-sync.c#L93-L108

[link2xt]

I have looked into UID validity values.

Here is an example core log:

2024-07-14T12:27:33.032Z	core/event            	INFO	""	1	"src/imap/select_folder.rs:227: uid/validity change folder INBOX: new 139/1720880574 previous 3333/1718053341."

So Delta Chat core thinks UID validity was updated from 2024-06-10 to 2024-07-13:

>>> datetime.datetime.fromtimestamp(1718053341, datetime.UTC)
datetime.datetime(2024, 6, 10, 21, 2, 21, tzinfo=datetime.timezone.utc)
>>> datetime.datetime.fromtimestamp(1720880574, datetime.UTC)
datetime.datetime(2024, 7, 13, 14, 22, 54, tzinfo=datetime.timezone.utc)

However on the server dovecot-uidlist has 1718053341 in the first line, dovecot-uidvalidity contains 666769dd and there is an empty file dovecot-uidvalidity.666769dd next to it. 0x666769dd is 1718053341, so it seems this is still an old timestamp.

So it looks like UID validity is not actually changed in the files after all. But running this on the server reports new UID validity 1720880574, which comes from I don't know where:

# doveadm mailbox status -u XXX uidvalidity INBOX
INBOX uidvalidity=1720880574

[link2xt]

Ok, I figured out the problem, it was incorrectly configured mailboxes_dir that resulted in everyone getting a new homedir.