Q: my mail.com stopped working on my Snow Leopard Mac. can only get to mail via iCloud.

You need to set Mail up manually as described in this page:

Entering iCloud email settings manually in Snow Leopard or Leopard

That does not solve the problem. Already tried it.

The method I give does work, but something's going on at the moment, though I don't know how many people it affects - I'm getting my password rejected in the Mail application, though I can log in at icloud.com; this sort of thing usually means an authentication server error so hopefully they will sort it out eventually.

Edit: others were reporting the same thing, but someone reported it was now working so I checked again and it seems to be OK, so try setting up your mail again.