==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.8.3
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Debian 13 (Trixie)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
I followed the instruction found here: upgrade.debian.12-13.html on iredmail.org.

Everything worked fine, I could send and receive mails using Roundcube, but the password did not work on Thunderbird.
The reason was that "auth_default_realm" parameter was not set in the new dovecot.conf file. The username defined in Thunderbird was "username" instead of "username@myserver.xx".
I may have set auth_default_realm in the previous configuration and did not think about redefining it after the update.

The symptom was strange, the password worked everywhere but on Thunderbird.
I just wanted to give this information in case any other user would have the same issue.

Thank you for your work, I have been using IRedMail for many years and it is awesome!