Maybe your ISP or mail service provider has some problems or they are maintaining (fixing) their services at the moment.
Other possibility is that your line is heavily used (some P2P programs like eMule or Shareaza),but they usually don’t couse any troubles.
You can extend the timeout duration within your email program, in OE I think it is 60 seconds by default.
It doesn’t matter whether you connect by cable or dial-up if the mail server at your isp is down/busy, etc. for the timeout duration you get the warning.
Perhaps your email program is constantly checking for new mail, so it keeps checking the mail server, you could reduce the frequency you check for new mail.
Sending mail (via smtp port 25) could be successful, whilst receiving (pop3 port 110) mail may fail if the isp uses different mail servers for smtp and pop3.