From a user's point of view Bellsouth (or any other ISP) is just one place. In reality it is many dozens if not hundreds of physical locations with mail servers and for you more importantly login & password servers. The fact it sometimes works shows you have the correct login and password. Here is what I would do. Open Apple Mail's Preferences. Click on Accounts, highlight the Bellsouth email account in question, click the "-" sign to delete the account. Quit Apple Mail. Then open Mail preferences again and create a new email account. I fully expect Apple Mail will have a set of mail servers built in. It would be very unlikely the mail servers would be the same as you have. Just changing is very likely to solve your problem.

If that does not, call Tech support and ask them for some mail servers - tell them you deleted the account if they ask. As you undoubtedly know Bellsouth was purchased by AT&T. The old Bellsouth.net addresses are still valid, but they may not be using the newest equipment in the AT&T system. So if you get servers that look like pop.att.yahoo.com and smtp.att.yahoo.com that would be wonderful.

Gordon
Atlanta