Customer can't login into Roundcube webmail for email address created on IDN domain with hyphen '-'.
первый-домен.рф. Following error appears:
Invalid server name
FILTER_VALIDATE_EMAIL fails with valid addresses containing "--" twice. Additional information available on PHP.net Portal.
The behavior is caused by software issue PPA-3440.
As a workaround you can switch webmail client to
CCP > Mail > Mail Settings.