Mar 27 09:46:34 vpsXXXXXX postfix/pipe[8821]: 9D8AD20045: to=<contact@YOUR_DOMAIN.com>, relay=plesk_virtual, delay=55006, delays=55005/0.01/0/1, dsn=4.3.0, status=deferred (temporary failure. Command output: sendmail: warning: Postfix library version mis-match: wanted 2.9.1, found 2.11.0 sendmail: warning: the Postfix sendmail command has set-uid root file permissions sendmail: warning: or the command is run from a set-uid root process sendmail: warning: the Postfix sendmail command must be installed without set-uid root file permissions sendmail: fatal: execvp /usr/sbin/postdrop: Permission denied sendmail: warning: command "/usr/sbin/postdrop -r" exited with status 1 sendmail: fatal: YOUR_GMAIL.COM_ACCOUNT(30): unable to execute /usr/sbin/postdrop -r: Success 4.2.1 Message can not be delivered at this time )