Sometimes the illogicalities of Microsoft software baffles me.
There is a rule where ‘user’s domain’ (the bit after the @) can be added to the ‘trusted senders’ list but not the ‘blocked senders’ list.
the reasin this is illogical is that lots of spam use fals e-mail addresses but the domain is often the same from e-mail to e-mail so being able to block that particular domain would a) be very useful and b) save a lot of time and space taken up by 40 or so individually blocked e-mail addresses.
Firstly, in what product?
Secondly, possibly because it’s easy to get cavalier banning domains. I’d be very, very tempted to block AOL 
but know it’s impossible. Some people might make that mistake. Many products including many from microsoft - tend to baby people, good or bad.
Thirdly, have you considered using something else? I don’t know what, but I bet there’s a free replacement that does what you want
Whoops. forgot to mention that. I’m using Outlook.
I would consider using something else.
In Outlook 2003:
- Tools > Options > Junk Email
- Click the “Blocked Senders” tab, then click “add”
- Enter the email address or the domain you want to block. Apparently, you enter it as “straightdope.com” and not “@straightdope.com”.
I dunno how this works with other versions of Outlook. You cannot add a domain to your filter list by right-clicking on a message. This is probably because you don’t normally do this in your day-to-day email routines. I know I’ve never done it. But it could be added by them to the next version of Office - Office 12 - which they are starting work on soon.
Switch to Eudora. End of problem. (Also end of an almost infinite number of other problems). Categorize all or a fragmentary part of sender’s domain, present in a specified “From” header or in any other header for that matter, as sufficient to designate incoming email as “spam”.
Or categorize it as “spam” only if it’s addressed to one of your email accounts, but not others, for that matter.