Askimet works by checking links in every post against their spam database. This is being tested, and is used on many online forums.
my***.com is a mail forwarding company that has been misused by spammers and found itself blacklisted because of this. Nothing wrong with the company, its just the spammers once again rasing havoc.
The admin has the option of approving a post that has been held, and a message is supposed to be displlayed to the poster explaining what happened. I don't think that is happening yet. Thats the problem for a small operation, you have to fight the spammers (look at who is online now- 30% are likely spammers). Virtually all of them are blocked from posting but several get thru each day.