Mailserverlogin Postfix and Dovecot with UID

dovecot
postfix

#1

Hello,
as mentioned in https://docs.software-univention.de/handbuch-4.2.html#mail::management::users the primary mail address is used as login.
This behavior is different to all other logins where the uid is used.
Is there a reason why we use the primary mail address and not the UID?
Is it possible to configure postfix and dovecot that uid and/or mail address can be used for login?

root@mail:/etc/dovecot# univention-app info
UCS: 4.2-1 errata139
App Center compatibility: 4
Installed: mailserver=11 open-xchange-text=7.8.4-ucs1 oxseforucs=7.8.4-ucs5
Upgradable:

Greets
Matthias Hütter


#2

The related bug with more information is mailPrimaryAddress vs. uid as username.