Unable to connect SMTP server:smtpout.mail.zoho.com Reason:Unknown host:

I have 2 accounts in my domain distribution.kinolife.eu. First one is admin account ind second one is regular user.
From regular user account I cannot send any mails. Every time I get "Unable to connect SMTP server:smtpout.mail.zoho.com Reason:Unknown host:" error. Please advice