Then the first thing I would do is check the network connection. Maybe you have a wrecked network card, switch port ot et cetera. Try running another protocol, like FTP, over the same connection. If you get similar errors you can rule out dovecot.I did run a protocol analyzer trace on the TCP transaction, when the POP3 clients were connecting and discovered a lot of Re-Transmissions and Duplicate ACK packets.
JC
