To support EMail address, I think. If it's not showing up, is local MTA blocking sending or is the SMTP server where the mail is to be delivered blocking. Some mail systems are set to 'paranoid' mode these days (and rightfully so considering) such that if the sending address (the @server part) doesn't have verifiable SPF, valid reverse DNS, or other MX records, it's blocks/denies.
Check your server logs ... maillog if you have one ... to see if the MTA sends and if the rec. server denies.
'spirit of sharing', Ken