This is an excerpt from the mecury mailing list at BAMA.
Clients may report "socket-error: 10053, errornumber: 0x800CCC0F" regardless of client program used.
The winsock connection is being dropped by Windows itself due to malformed communication (i.e. tcp/ip packet size).
Most probable cause is your antivirus program or your firewall, or anti-rootkit or anti-spyware software, interferring with the traffic to the smtp/pop3 server. The problems have been reported by systems running windows 95 all up to Vista (aka Windows 6).
Recent fixes can be available and we recommend that you search for the keyword: 10053 at the site of your antiviral vendor.
references: Microsoft KB, Symantec, McAfee, ZoneAlarm, Norton