We have two IMAP email accounts which use smtp.outlook365.com to send emails via Thunderbird 115.7.0 One account stopped being able to send about six months ago but I could not resolve the problem with either your help pages or by comparing with account settings with the address which could send emails successfully. This week the second account can not send emails either. Both accounts receive all incoming emails. We have Kaspersky VPN and have switched this off without it making any difference. Our smtp settings are:- smtp.office365.com port 587 STARTTLS Normal password (I have tried OAuth2 and No authentication but none helped) ''user.name''@outlook.com The error message on sending says :- Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) smtp.office365.com timed out. Try again. Any help would be appreciated.