KMail "Socket operation timed out"

[Timothy Murphy]

I'm running KMail under Fedora-15 on a laptop
with an "Onda MC833UP" (ID: 1ee8:0014") broadband dongle.

Everything works fine (eg firefox, knode) except KMail,
which I'm using to collect email from an IMAP server.
I get an error when I try to "Check Mail",
I get the message "Could not connect to host ...
Socket operation timed out".

I should say that everything works fine
when the internet is accessed with WiFi.

Also I can telnet 143 and get the message
"* OK Dovecot ready"

Has anyone had this problem when using a dongle?
Or can anyone suggest a possible solution?