Direct Spam

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.