Monday night I was out with a few Techies and the conversation got around to “how most ISP block port 25”, “hosting companies”, and “SPAM”.
During our discussions I mentioned that a while back my hosting company would get added on to one of the trigger happy Blacklist servers for 24 hours at a time. Needlessly to say I talked to tech support at my hosting company and they would do everything in their power to fix the situation. This included changing the IP address of the SMTP server so that email would get sent out again, they were great from that perspective.
I don’t remember how or who suggested looking at a SPF record: it would have been either the hosting company or Rick Claus https://blogs.technet.com/canitpro/default.aspx or https://www.microsoft.com/canada/technet/community/meettn/default.aspx# however I did some quick research and found this introduction to SPF records https://www.openspf.org/Introduction
Now everyone knows that I’m not an Exchange person but…. I saw the benefit of this right away. I opened a ticket with my hosting company and asked them to tell me what should be added to the SPF record.
Since adding the SPF record, I have had no messages blocked as SPAM that I know of, so talk to your hosting company and get a SPF record added to your site.