Since Thunderbird is working properly, you might pursue this with your email provider.

My ISP was the first person I tried. However, my web mail is working perfectly. The issue is Thunderbird not downloading from my ISP to my desktop.

As I stated above, if I close down Thunderbird and re-open it all my emails download fine. But then stop downloading until I close TB again and re-open.

i have no solution in mind, but what are the server settings for that account, the ones that specify checking for messages?

Set to check at start up and then to check every 1 minute thereafter.

The account was working perfectly til 10 days ago and I haven't changed any of the server settings.

My other email accounts on Thunderbird all have the same settings and are working perfectly - it's just my primary email which isn't downloading.

I'm baffled.

You might check for patterns. As i understand, you have five accounts with the same ISP. Could it be that there is a limit with the ISP? However, I have no solutions. I'm also baffled.

Unlimited email account, and it's been working fine for years. I don't know what's changed to cause an issue just with one email address and not the others.

I've changed the download from every minute to every 2 mins and will see tomorrow if that has helped.

Changing the download time hasn't helped.

Can Mozilla support offer any solutions please?

This does not appear to be a Thunderbird issue. With five concurrent accounts, the issue may lie elsewhere. But network communications is not a specialty of mine. For whatever it's worth, here is more info on IMAP connections: http://kb.mozillazine.org/IMAP:_advanced_account_configuration