I have used four separate email accounts within Thunderbird for at least that last three years. I am now on version 45.2.0. One of these accounts has stopped working because of an authentication failure that appears to be incurable, except by changing the password to remove characters that are obtained by a combination of the shift key with a number (in the row above the letters). The password I used was N2*h7F-ki£m , which has two such characters: shift+8 and shift+3. The password worked fine when logging in via webmail so it wasn't a server error. I always copied and pasted the password to avoid finger trouble, and it was correctly logged in Thunderbird's saved password facility. I tried the same password on another client - Mailbird - and that also worked fine. My ISP did some work on the problem too, and came up with the following suggestions: 1. Change server name 2. Double check all the security settings 3. Change the account to IMAP (from POP3) None of these resolved the problem. They did check the thunderbird error log site and said an error with the £ sign had been sorted. Looks like it may not have been. Now I have changed my password to fully alphanumeric again, Thunderbird is working normally. Looks to me like a problem remains - and with us all being urged to use very complex passwords with special characters - its going to arise again. I do have a log file from Thunderbird if that will be of any use to check this out. Richard