Running "outlook express" [a eMail windows program] results in this error:
"An unknown error has occurred. Account: 'name', Server: 'mail.yourdomain.com', Protocol: POP3, Port: 110, Secure(SSL): No, Error Number: 0x800C013x"
Possible cause:
It appears the "inbox" is limited to approx. 2500 eMails, depending on total size of attachments.
Possible solution:
1.) Create new folders. (right-click in the left-hand folder field, and select "new folder".)
Name them "Pictures, Inspirational, Humour, Dirty... etc."
Move existing eMails to one of these new folders. (Preferably to a matching folder category.)
[Click and hold on each eMail, and drag to the folder.]
[Holding down the 'Control' key while clicking eMails, allows multiple selections.]
[Holding down the 'Shift' key while clicking an eMail, then clicking another one further down, allows selecting a range of eMails.]
Repeat until the inbox is a considerably smaller size.
Attempt to download more eMail.
2.) Click 'Tools', click 'Options', click 'Maintenance', select 'Compact Messages'.
This will take some time.
When complete, attempt to download more eMail.
3.) Refer here for more advanced solution.