sending mail problem

We just started having problems emailing a company we work with and
regularly exchange emails with. In the GWIA logs I'm seeing
"deferring message" and "420 TCP write error". I looked up their
domain ( at I see two hostnames listed.
The one with Preference 10 says no A record. The one with Preference
100 does have an A record. That doesn't seem right. Is that the
issue here or do I need to be looking for something on my end?



  • A 420 is one of those vague return codes that means nothing and everything. This could be as simple as them greylisting. Their mail is going through, so it's hard to say. One thing you could attempt is to see which server it is attempting that gives you the 420 (if you are lucky enough for it to be the same one every time), and put the IP address of the second one in a route.cfg to see if it will go through without trouble.

    The other thing might be your own GWIA. While there is really nothing in the RFC that demands that your PTR match the helo from your GWIA, if it does not, the other side might be dropping the connection.

    So, the answer here is, it could either be you or them, but if it's you, it will have to do with your PTR almost certainly.