I have my website hosted at one location, on a server that also accepts email, and I use Google Apps for mail as my email provider. I've had no problems in the last 18 months, and no reports of email being lost.
This week however, someone using Hotmail has tried emailing me. 25-50% of the emails they send are returned to them, with a "550 relay not permitted" message.
My MX records are correct, and checking the Exim logs on my web server I see that Hotmail is trying to send emails to the A record, because this server can accept email. This appears to be a known problem with Hotmail.
As I can't disable the webserver from accepting mail from Hotmail (since other people use the web server as their email hosting), is there a solution?
Best Answer
Hotmail fails to use proper DNS rules. Hotmail will always try to deliver to the domain's A-record first and will ignore MX-records. If the domain A-record accepts a connection (eg. it runs a mailserver) it will try to deliver the email, which in most cases will not be an issue if the webserver and mail server are the same box.
However, if an domain uses a different mailserver Hotmail will still try to deliver mail to the domain's A-record. If the machine gives a 550 Relay denied Hotmail will fail to deliver the mail. It does NOT try the domain's MX-record.
THe only work around is to firewall port 25, so Hotmail is unable to connect to your port 25. If that fails hotmail will try to resolve the MX-records.
This has been an issue for years, but Hotmail is ignorant.