From Computer Tyme Support Wiki
Spam that Bypasses our Filters
So it's been several days and you notice that some spam is still being sent directly to your old server even though all your MX records point to us. So you're asking yourself, "How does this happen? How do they know where my real server is?"
There are two reasons for this. The first is that spammers cache old MX records for far longer than they should. Sometimes it takes weeks for their servers to forget the old MX records. But the other reason is far more common. It's caused when your email server is the same IP address as your domain. For example, if your web server is domain.com and your email server is also domain.com then spammers will sometimes try to send email directly to your server and thus bypassing our filters. But there are things you can do to stop it. but it might take a little work.
- If you have more than one IP address the easy thing you can do is define a new host on another IP and call it something like mail.domain.com. Make that IP accept email from our servers and close the email ports on domain.com and your direct spam problem will go away.
- If you have just one IP address you can close of port 25 and open up the submission port on port 587. You can use that port to send your outgoing email. We can forward email to you on that port or some other unknown port. That will stop your direct spam.
- If you can't set up the above solutions then you can look at the messages themselves to determine of they have our junkemailfilter.com headers. If the message hasn't passed through out filters you can just black hole it. We always label our forwarded email with this header.
X-Spamfilter-host: pascal.ctyme.com - http://www.junkemailfilter.com
If the header isn't there then the message is spam.
So - if you decided to use a new IP address or want to use and alternate port then contact us at firstname.lastname@example.org and we'll set it up on our end.
What about only accepting email from our hosts?
Many people ask me, What are your spam filter host addresses? Why can't we just accept email only from your hosts? That's is a good idea except that we sometimes change IP addresses and add new servers so you can't rely on our host list staying constant.