They would claim that, and they may be partly right. You need to understand first that when an email client (such as Thunderbird) establishes a connection to a POP mail server, a 'lock' is put on the server so that no other client can access that account at the same time. If all goes well, when the first client signs off a concluding signal is sent, and after a period of time (10 - 15 mins is common) the lock is released and the server is once again available. Sometimes, though, things don't go well and you end up with an ongoing lock. If you search for 'pop lock' on the internet you'll find several possible causes listed. One is having more than one client trying to access the same account, e.g. your computer and your phone. Another is trying to log into the account too frequently, i.e. multiple attempts in a short period. Another is a Windows virus attempting to send mail from your account -- see here for someone who had exactly the same error message as yourself: http://askubuntu.com/questions/29156/what-does-in-use-account-is-locked-by-another-session-or-for-maintenance-try

I am still having the issue described above. I disabled my smart phone to not receive any emails. That was the only other app that was accessing my email account. Still have the problem.

Thanks for you help. Ron in Georgia