I'm sure Taleman are right. It's an external account sending mail to you
What the logs say?
You can have old PHP 5 in newer Linux releases:...
Normal webmail access shouldn't have any problem.
If you want to access with the master password you should append :admin to user mail on...
Just clic "editar identidades" next to the from, and delete the :admin.
You should do this only once time for every account
You can't see passwords but you can set master password for dovecot and login with it to all accounts:...
Why not shared them here?
Do you see any error in the screen if you enable display_errors?
Try adding lines one by one until it fails to find the problematic line
Phpmyadmin only provides a web interface that make easier to work with mysql databases. With no phpmyadmin you could work with mysql from command...
It's the default behaviour in MySQL 5.7 to autologin in without password.
Check step 3 here to change this
For future reference.
To copy all mails from one account to another, especially if they are in different servers, you could try:
Try disabling SSL cert on site B
Will try it.
Separate names with a comma.