I spoke with 1and1 (my supplier)
it explained that on pesk onyx (which provides 1and1) can not be accessed
to Tools & Settings> Updates and Upgrades.
on the shell I gave this command:
#plesk repair all
it found an error:
There are files or directories with suspicious permissions in the
root directory of the domain 'xxxxxxxxx.yyy' ........................ [WARNING]
To see more details, run the command in the verbose mode: plesk repair fs -verbose
#plesk repair fs -verbose
Checking virtual hosts' file system
There are files or directories with suspicious permissions in the
root directory of the domain 'gmdental.eu' ........................ [WARNING]
- /var/www/vhosts/xxxxxxxxx.yyy/httpdocs/wp-config.php
Error messages: 0; Warnings: 1; Errors resolved: 0
I deleted wp-config.php file and I repeated the commands:
#plesk repair all
Error messages: 0; Warnings: 0; Errors resolved: 0
now this command
#plesk repair installation
but I still can not configure email boxes