Mailserverlogin Postfix and Dovecot with UID

as mentioned in 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

Matthias Hütter

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