what mail provider... What I have seen recently related to yahoo, and historically apple products were implicated because their mail programs had no connection limiter, they just use them all up to improve the apple products apparent performance.

Response appreciated Matt. My situation involves an existing Waitrose / John Lewis email address, inherited (purchased) by Plusnet who gave me a new "default" mail.plus.net (POP Mail Server) address. But allowed me my waitrose.com (IMAP) address for all social mail. However, I can logon to both mail-boxes (fault-free) via my Browser. I email from only one Home PC , so my traffic is always pretty low.

I note a number of other contributors with the same problem over a long period, but not any I found with a consistent route to avoiding it.

By the way, I always thought that my waitrose.com address (even after the Ptusnet/BT take-over) was also POP. But not now for some reason - although my Provider confirms that my Server options and addresses are typical and correct.

Furthermore Matt, Although I have a Gmail address, I no longer use a mobile for physical reasons so that won't be hogging resources presumably. The only time Tbird seems to play ball is briefly around the time that new mail has just been downloaded. Anyone else with a view or suggestions?

re : I have tried changing the existing number (which is 5) to alternative numbers between 1 and 8

5 is set by default in Thunderbird. Problems can occur when using Courier server, so you need to lower it. Courier IMAP servers typically have a limit on the number of connections they can cache which is much lower. If you have one Courier account you need to lower the Thunderbird setting to 4 or less. If you have two Courier accounts you need to lower the setting in each account to 2 since it's 4 connections per TCP-IP address.

I believe Plusnet uses Courier.

Set it at 1 or 2.

You will know whether it is POP or IMAP by looking in Account Settings Select 'Server Settings' and on the right side it will say: Server Type: POP Mail Server or IMAP Mail Server. POP mail accounts can only access server Inbox to download mail to Pop account Inbox. IMAP account store all emails on server and folders synchronise with server to display what is on server.

re :, I no longer use a mobile for physical reasons so that won't be hogging resources presumably. Assuming phone is switched off or mail account removed.

It also assumes you do not have some other email client set up. I have come across cases where someone previously set up a mail account in Outlook email client. Somehow, it was still running in the background much to their surprise. So, do check your computer if you previously used a different email client.

How frequently does the IMAP account check for new mail ? Account Settings > Server Settings for imap account select checkbox: 'Allow immediate server notifications when new messages arrive'. The IDLE command is a extension to the IMAP protocol that lets the IMAP server notify Thunderbird when there is new mail by sending a command over the existing TCP-IP connection. If your IMAP server supports that you don't have to manually check for new mail or have Thunderbird poll for new mail every x minutes. So, if the server PUSHes emails as per above setting, - then you may not need to keep checking server.

'Check for new messages every X minutes' - If this is set to 10 minutes or less then suggest you increase it to say 20 minutes just in case the PUSH Idle connection fails OR better still uncheck that checkbox to see if the server will PUSH emails.