Thunderbird does not reject passwords that will be the server you are attempting to connect to which is objecting to something being wrong. It could be the password is wrong or password is correct but not for the other server settings. More info is needed. What version of Thunderbird are you using ? What server are you trying to get a connection ? gmail ? yahoo ? aol ? etc What server settings are you using ? You could simply upload images that show Account Settings > Server Settings and just scrub out the email address/username. It would also be helpful if you could upload an image of the error message. In the meantime please check to see if you have recently enabled a VPN. Some Anti-Virus now provide a VPN and in several cases I've come across people who did not realise it was there let alone enabled. Please switch it off as many server do not like it as it hides your real IP address and server may think you are a hacker - so it blocks access. Firewall Access Firewall which may the defaul on computer or one controlled by an Anti-Virus. Thunderbird program must be set up as an allowed program to ensure nothing gets blocked.