re : told by several people they had had suspicious messages purporting to come from me. That could be some nefarious person who has just decided to send emails that look like they are coming from you. Usually, they get bored after a while. It's important no one responds to those emails because it's likely they will go to a different email address confirming your email address is live. Sometimes those emails contain content which is designed to include remote content and the sender has tracker content in email. So sender is trying to see if the people who received the email were live email addresses. It does not necessarilly mean that person hacked your webmail account. They are just abusing the email address. This is the most common. However, it is sensible to access webmail account and modify the password. That's the password you would use to access the webmail account itself. In addition, you may want to get a new app specific password which you would then only use in Thunderbird. If you are concerned whether someone has installed something on your computer and it's sending keystrokes to nefarious person then this may imply they already know about your updated password. Exit All programs Restart computer in Safe Mode. Run scans. When completed - if nothing bad found then you know all the passwords you set up will be perfectly ok. Thunderbird will not be able to download anything if emails are not being received by the server. It's possible you have too many emails on the server - especially if loads of emails were getting sent back to your email address as sender did not exist etc. Maybe server quota is full so physically it cannot receive anything. I would check this first. Log on to webmail account and empty the Junk and TRash folders - check the 'Sent folder as it may have tons of emails which you did not send. Basically create some space on server. Please note - anything you remove off server will also get removed from any Imap account.