Fishy scenario. And don't you love it when these folks reword and thus reward your own complaint by tossing it back atcha in a ridiculous restating of the obvious! Sue has a certain genius for this sort of troubleshooting herself, but I have no urgency to rag on her this early in the morning, so off we go to your problem. I certainly don't have a clue what's besludging the Fastmail system short of that pesky Y2K bug, speaking of which I can relate a recent problem of my own. My web log stats program which fraternizes with WebStar and which I provide free of charge via a web interface with user ID and password to 'XusNet clients caught that blasted bug. A fix was issued after my sister (a client) discovered a problem. The beta upgrade fix was acknowledged front and center on the vendor's website sometime in the middle of January, a quick download and installation, and the problem was solved. What dismayed me was that I didn't get an email from them alerting me to the bug, or its fix.
Secondly, and closer to your own email problems is that sometime last month my own 'XusNET mail server fell victim to a mail attack where some unscrupulous cell phone mass marketer was hitting me with thousands of mail relays every minute of the day. Of course I caught it when my daily logs piled in exponentially against the normal rate of one per 24 hour shift. As I was frantically hurrying about trying to solve the problem, soaking up the manual wisdom, toggling and what have you, I also got a mail warning from a website dedicated to such SPAMMING PRACTICES telling me I had been placed on a blacklist which identified sites which allowed such despicable email relay practices, and could result in other sites refusing to handle ANY mail requests from 'XusNET servers. Where's my secret decoder ring?
Fortunately I had read about this very site a couple of months ago, and with that heads up in mind, wasn't totally panicked by the news, but grateful to be part of a great checks and balances loop. I solved the problem partially, but then in a mail relay to a client (again, my sister) another problem in my config showed itself. She was being allowed to relay mail. I think I have fixed it, but she has been slow in responding to me after I suggested a particular test at her end of things.
Oh well. . .
Oooh la la! One might be forgiven, Steve, in thinking Fast.NET would be ahead of the curve on this one.