my system has worked with the "SMTP after POP3"-mechanism. But nowadays it doesn't work. Can everyone tell me what the problem is?
I'm not sure what your particular problem is, but 'SMTP AUTH' is a better way to go.
Someone else on the list was having trouble with increased load on his system causing POP users to get errors. This is caused by locking issues with the files used to track SMTP after POP.
Switching to SMTP AUTH takes care of this problem. The downside is customer education. I was lucky enough to have switched to AUTH with a small userbase. Now, when adding new customers, it's easy enough to explain how to set it up in their email clients.
As for your issue, check the permissions on the tcp.smtp and related files. If they're owned incorrectly, the .cdb file can't be rebuilt.
QmailAdmin: http://qmailadmin.sf.net/ Vpopmail: http://vpopmail.sf.net/
Info on the Sniffter hand-held Network Tester: http://sniffter.com/