Postfix and dovecot login wirh UID

I want to login with uid instead of the mail.adress@domain
how can i fix it because the bug is reported since 2015 and nothing is fixed in the actual errata of the ucs server.

Just to save time for everyone else who reads this.
OP is most likely referring to Bug 37814 - mailPrimaryAddress vs. uid as username

This bug has currently no priority, as almost everyone wants to use the email address for login.

A solution that is not safe for updates of the package univention-mail-dovecot for you would be to comment out the line 12 (print auth) from /etc/univention/templates/files/etc/pam.d/dovecot.
To comment it out, prepend a # to the line.
Then run ucr commit /etc/pam.d/dovecot