Lately I have been having trouble sending messages. I haven't changed any settings, but I did recently upgrade to Windows 10. The problem takes the form of very slow sending once I hit 'send'. It stays on the 'sending message' dialogue box with Status as 'Connected to smtp.mail.yahoo.com'. Sometimes it will take 5-10 seconds, sometimes longer. The issues seems to have been getting worse and worse, until today I was unable to send anything. Eventually the sending will time out wth the message 'Login to server smtp.mail.yahoo.com failed. And then 3 options - Retry, Enter New Password, Cancel. I first checked the Yahoo servers by logging in and sending messages - no problem there. I then checked all my Thunderbird settings - no problem that I can see. I tried uninstalling everything, starting with a brand new profile and creating the E-mail account from scratch - same issue. I tried deleting my smtp password from password manager, and the next message I tried to send went straight through. Subsequent messages end up with the same issue as before. I also tried switching off Comodo, in case that was causing an issue. I tried sending mail from a hotmail account within Thunderbird, and that seemed ok. I have 3 Yahoo accounts in Thunderbird and they all have the same issue. The problem seems to be intermittant, with varying degrees of delay, but mostly it just times out. Please help! :)