I don't have an answer but I have a theory based on what happens with my gmail. Mine typically arrives around 8 hours late - I'm in the UK, it seems like some kind of regional delay. This has been going on for a year now.

Thank you. I am in the UK, too, but this is a new problem. I'll continue to see what I can do about it.

Are you talking about a Pop or Imap account ?

Do you have an Anti-Virus which is allowed to scan files etc when either downloading mail OR whenever a file is opened ? Advise: to rule out Anti-Virus causing delays - Access AV and set up an exception to not scan anything in your Thunderbird profile. Usually located here: C://Users/username/Appdata/Roaming/Thunderbird

Gmail can also be a pain for those using POP accounts. If you do not periodically access the webmail account via a browser and delete old mail and also previously deleted mail from the 'All Mail' server then gmail can be a nuisance and deliberately stall downloads. Note only do the following if using a POP account in Thunderbird because those emails in a POP account are a completely independent copy on your computer. Access the gmail webmail account and delete the old mail from 'All Mail'.

Do not attempt this if using an IMAP account as you will lose emails from Thunderbird because an IMAP account can only display whatever is on server.