[qmailtoaster] UIDVALIDITY value changed during Courier-to-Dovecot migration

[Quinn Comendant]

I've done a test upgrade of a cloned server from Courier to Dovecot. So 
far, it's working well with most email clients, but when I reconfigure 
MailMate to connect to the new server, it gives me this error 
([screenshot](https://send.strangecode.com/f/screen-shot-2022-10-18-at-23-51-55.png)):

The so-called UIDVALIDITY value of the mailbox “INBOX” has 
changed. MailMate has to resynchronize the mailbox, that is, purge the 
local cache and refetch the messages of the mailbox.

I'm pretty sure I ran the 
[courier-dovecot-migrate.pl](https://raw.githubusercontent.com/dovecot/tools/main/courier-dovecot-migrate.pl) 
script successfully.

I'm connecting via IMAP, so I don't think the `pop3_uidl_format` config 
option comes into play here. Anyways, the [Dovecot migration 
guide](https://wiki1.dovecot.org/Migration/Courier) says: *“With the 
v1.1+ migration script you can use any pop3_uidl_format, because the 
UIDLs are stored directly in the dovecot-uidlist file.”*.

I just let MailMate resynchronize my test mailbox, and it worked fine 
after that (it only asked me to do it once). However, I would like to 
prevent any of our users having to resynchronize mailboxes, if possible.

Regards,
Quinn