Look under Tools -> Account Settings -> Server Settings -> Advanced and uncheck Use IDLE command if the server supports it.

Thanks but at Tools>Accounts Settings>Server Settings there is only one Advanced button and that refers to 'Message Storage' not 'Incoming mail'

Please clarify, is this a Pop or IMAP mail account?

Hi, Its a POP account

In Account Settings > Server Settings, are there no checkboxes for server settings to check for new messages at startup, check for new messages every X minutes, and automatically download new messages? You should be able to disable those things.

Thanks - Yes its true there are checkboxes for determining how messages are downloaded & they have been set accordingly. Although this works on one computer on another computer it seems to have no effect. I am wondering whether the program on that computer has a glitch & either the program or at least the accounts need to be reinstalled.

Another problem only on that computer is that after messages are downloaded & deleted from the server, they have also disappeared on that computer after rebooting it.

Sounds like a problem with the profile.