On 6.5.2011, at 4.25, Dave Yost wrote:
A user on our server for some reason didn't have a home directory. As a result, the pop3 server was complaining. Apple's Mail app reported that the server said:
The attempt to send data to the server "(null)" failed.
It would be nice if the server would say something to the effect that the connection failed because the user account has no home directory.
I'm pretty sure Dovecot said something different. I don't know why Apple Mail would only say (null). Dovecot also should have logged something in its error log.
You could try reproducing it. But instead of connecting with Apple Mail, connect directly with telnet and see what Dovecot really says:
telnet pop3.example.com 110 user foobar pass secret
http://wiki2.dovecot.org/TestPop3Installation has more possibilities