Mozilla Thunderbird mail problem

[dxer]

One client is using mail client Mozilla Thunderbird and he is having problems with receiving mails.

The problem is that he has incoming mails and Mozilla is reporting that there are not new mails to receive. When going to webmail, there is confirmation that mails are there.

I told him that the best test is at that time to test with Outlook Express so we can see if this is general problem or just Mozilla.

But , I would like to know if there is known problems with Mozilla or in general with this kind of problem , and of course how to fix it

thanks