Changes

You can setup [[Postfix]] to send as an Internet Site. And you can even use it to send mail through an external service like GMail (called 'smart hosting'). Once you do, you certainly need to add or reconfigure your domains [[SPF ]] record in [[DNS]]<ref>https://www.digitalocean.com/community/tutorials/how-to-use-an-spf-record-to-prevent-spoofing-improve-e-mail-reliability</ref>.  If you just 're not outsourcing everything through a third party, you'll want to use the MX records implement [[SPF]] and A records to control who is valid, then <code>"v=spf1 mx a -all"</code> is the record that works. This [http://www.spfwizard.net/ wizard[DKIM]] can help. Once you're done, you can check on things with <code>nslookup -query=mx</code>