SMTP Authentication for MAC clients Certain clients on the Macintosh platform may have problems using the SMTP Authentication feature with MailSite Such users should be instructed to alter the email client to use the % instead of the @ sign. Typically when checking the option "my outgoing server requires smtp authentication" we tell the client to use the same settings as the incoming server account credentials. You will need to explicitly provide the login credentials in the client and replace the @ sign with a % sign: So joeuser@newdomain.com should be replaced by joeuser%newdomain.com