Thunderbird Community Forum

Can not send emails through RoadRunner Mozilla Thunderbird. Can receive. Can send in Spectrum.net, so email account is working properly. Can send and receive with android phone, just not Mozilla. Can not check for latest updates.

Things have suddenly disappeared. My sent file is gone and I have searched and can't find it. Tonight I went to send an email and the tab for doing that is also missing. I tried uninstalling and reinstalling with no success. What's wrong and how do I fix it?

bob.fannon

Feb 14, 2026, 13:01 CST

I have used Thunderbird for a number of years with Plusnet (using POP settings) in the UK. However, Plusnet has transferred their support to a company called Greenby who have made a hash of it and offer very poor support. So, I want to use Outlook as the mail server but I am unable to send any messages via Thunderbird to the Outlook server. I can however download messages with no problems. The error message I get is :- Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.office365.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'

My default Outgoing Sever settings are :- Server Name : smtp.office365.com Port: 587 User Name: bob.fannon@outlook.com Authentication method: OAuth2 Connection Security: STARTTLS

I have tried deleting the Thunderbird account and re-creating it but still got the same result. I also tried to use my old Icloud account ( having first setup my App Specific password) but got the same result.

'URGENT I can receive emails but cannot send emails. Keep getting them back "undeliverable" but they are to my regular email addresses. I have checked and recheck the format for sending they are correct. This occurred around 2nd April As I am making arrangements for a family member's funeral this is an urgent matter.

As of today (6th Jan '26) TB claims there are no new emails. This is incorrect, they are there on Gmail, and have appeared on my iphone. Can't find any way of getting TB to play nicely with Gmail, any suggestions for a work round gratefully received.

Apparently MS has changed something in their OAuth2 and Thunderbird has yet to catch up. I've seen several other questions regarding this, but no workable solutions, just silly replies. Is TB actively working on a solution or am I now forced to install Outlook?

Thunderbird email send stopped working something like three weeks ago. I am using Fedora 43. What happened to cause this send problem? I had been using Thunderbird for a very long time with no problems. I am using Mozilla Thunderbird 147.0