1. Is the Internet slow for you in general? Can you watch a YouTube video without it buffering a lot? It is the end of the month, and perhaps you went over your allotted data for the month, so your ISP has slowed you down.

2. Check the security on all the devices that are using your Internet connection. Make sure the antivirus and firewalls are working and up-to-date.

3. Run scans with additional anti-spyware and anti-malware scanners. I recommend using the free versions of both Spybot Search & Destroy and Malwarebytes Anti-Malware.

4. Double-check your e-mail server settings. Go to your e-mail provider's website and search for "email server settings". Find the page that has that info and compare it to your settings in Thunderbird. Server settings sometimes change. Thunderbird menu: Tools: Account Settings: For incoming e-mail: Select "Server Settings" on the left side under your e-mail account, and the settings are on the right side. For outgoing e-mail: Select "Outgoing Server (SMTP)" on the left side, then select the server you want on the right side. Click the "Edit" button to change the settings.

5. Do a check disk of your hard drive: Open "My Computer" or "This PC", right click your C: drive and choose "Properties" Open the "Tools" tab. Click the "Check" button under "Error Checking". Follow the instructions. Reboot the computer.

Thanks. Sorry for the double posting. I thought I'd lost the original somewhere! Everything works as normal. Everything has been checked and is working normally. The rest of the interweb is fully up to speed. It's just Tbird that's slow. I've spoken to my ISP this morning. I don't understand things but he logged on at his end to Microsoft Outlook (I think that's what he said) and he claimed that my mails were downloading speedily. I don't appear to have Outlook on my machine but wouldn't want to confuse the issue further by starting to use Microsoft stuff.

Try running Thunderbird in safe mode. Hold down the Shift key when double-clicking the Thunderbird shortcut. In safe mode, all the add-ons are disabled.

Try disabling the anti-virus on the computer temporarily.

Thanks for your help. Nothing I did had any effect. But I heard on the grapevine that my e-mail host was having technical problems which have lasted most of the week. Pity it's almost impossible for Joe Public to get to speak to them. They seem to have got to the bottom of the problem and everything is now back up to speed. Looks like it wasn't a Thunderbird problem after all.