I am concerned my mail server setup may cause some ISPs to reject mail that is sent by it.
I am using Postfix to send mail for a web application, light load, user notices. It also sends cron notices and "monit" alerts. It is for sending mail only. I guess it wants to be "null client".
The postfix server and webapp live on the same box. The webapp builds the "to" and "from" email mail headers.
Server: 123.foobar.com Website Domain: mysupersite.com
Mail that is getting sent by postfix has: from: email@example.com HELO: 123.foobar.com (18.104.22.168) (I am not sure this is enough header information to describe my condition)
I have read that some mail servers will reject incoming mail where the "from" email address domain does not match the sending servers domain...
To throw a twist into the mix, this server does not have a dns record. I have read that some servers are configured this way on purpose.
For example: "dig 123.foobar.com +short" & "dig -x 22.214.171.124 +short" give no answer for my server domain.
So there seems to be no way for a mail server to see if HELO is telling the truth. IF the accepting mail server is even checking.
As of now, mail is getting sent as I describe and it arrives to its destination but only a small amount of test mails.
But is this the right way? Is there a better way? Should I send my mail through a relay host? I have more questions than answers. Please help!