Situation: Web server that sends out mail. Configured with SMTP service for this purpose.
Problem 1: Some of emails being relayed by the local SMTP service were failing with “550 not local host gmail.com, not a gateway” (where gmail.com is the domain of the mail in this example). This was domain specific.
Problem 2: Some relay SMTP servers were refusing to take mail with a “greylist” warning. (They would work on subsequent tries).
Firstly, I made sure the “from” domain had valid ANAME Records. No result.
Then, I made sure the MX records of the “from” domain corresponded to the SMTP server. My logic was that the destination SMTP server was checking the MX record for the domain and failing when none in the list corresponded with the IP address that was trying to send it mail. No result. But I did get incoming mail on my pmgconnect.com and pmgconnect.co.uk domains to route through my web server (downside I had to open up POP3 port in the firewall).
Then I investigated and found that the SMTP server was getting a different MX record for the domain (in this case gmail.com) than any this MX record lookup tool gave me. As I was writing an email to the dedicated server host to tell them that something was fishy with their DNS lookup, I decided to check their site for the correct settings…
Yes, all this because I had the wrong DNS settings on my network connection. Probably in an email from the hosting company that I ignored. Well, it all works now.
I’ll watch the “greylist” problem but I suspect the MX record of the sending server may be responsible. Not sure. Could be because the emails being sent had no “from” as they were automaticlly forwarded error reports. Not only will I be getting far less of them, but thier destination domain pmgconnect.com, is now the local server so they just sit and wait for my POP3 pickup.