I-Thunderbird Community Forum

Hello Thunderbird Support Team,

I am experiencing a persistent SMTP authentication failure when sending emails from my personal Outlook.com account using Thunderbird.

My configuration:

Operating system: Windows 11 Pro (64-bit)

Thunderbird version: 159.0 (32-bit)

Account type: Personal Outlook.com account

What works:

Receiving emails via IMAP works correctly.

Sending and receiving emails through Outlook.com webmail works correctly.

My other Microsoft email account works in Thunderbird.

What does not work:

Sending emails from my new Outlook.com account through Thunderbird consistently fails.

The SMTP server returns:

535 Authentication unsuccessful – SmtpClientAuthentication is disabled for the Mailbox.

Outgoing SMTP settings

Server: smtp-mail.outlook.com

Port: 587

Connection security: STARTTLS

Authentication method: OAuth2

Username: Full Outlook.com email address

Troubleshooting already performed

Checked all SMTP server settings.

Verified that OAuth2 is selected.

Removed previously saved authentication credentials.

Repeated Microsoft OAuth2 authentication successfully.

Retested sending messages. The same error persists.

Thunderbird's Error Console confirms that the failure occurs during the AUTH XOAUTH2 authentication exchange.

The server explicitly reports that SmtpClientAuthentication is disabled for the Mailbox.

Questions

Is this a known Thunderbird issue affecting SMTP OAuth2 authentication with personal Outlook.com accounts?

Could Thunderbird be generating an incorrect XOAUTH2 authentication request?

Can Thunderbird provide a more detailed SMTP diagnostic log to identify the cause?

Does this error indicate that Microsoft's SMTP service is rejecting an otherwise valid OAuth2 authentication request?

Is there any known workaround or can this issue be escalated to the Thunderbird developers?

I would appreciate a technical investigation rather than another general configuration guide, as the standard troubleshooting steps have already been completed.

Thank you for your help.

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My emails download ok from the server at Greenby. When I try to send a reply from Thunderbird, I get an error message: Login to server mail.madasafish.com with username anniedunn@madasafish.com failed.

I have tried entering my password, retry, nothing works - in the end I click cancel and get this message.

Sending of the message failed.

Unable to authenticate to Outgoing server (SMTP) . Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'.

Please can anyone help, it's very frustrating.

(I can send replies from the server)

I am getting this error message on one of my email accounts on opening Thunderbird, "Login to server imap.ionos.co.uk with username [redacted] @sackettfamily.info failed." How do I rectify this?

Chris Sackett

I set up a new Outlook.com account around a month ago. I initially had problems both receiving and sending but resolved that after enabling the IMAP option on the Outlook Web pages.

I have checked the SMTP settings and they are correct, and the connection test succeeds. Sending via the Outlook Web page works correctly.

For reference, I am using Thunderbird 153.3.1esr (64-bit) on Linux Mint.

habe E-Mailkonten bei 2 verschiedenen Providern seit es Thunderbird gibt. Seit dem letzten Update holt Thunderbird nur noch Mails von einem (immer dem gleichen) Provider ab. Stoppe ich das Programm und starte es wieder wird die Post von beiden abgeholt. Aber nur das eine mal nach dem Neustart.

Dear community,

Recently, I have received a message that looked like it was sent to somebody else (a situation very similar to the one described here). I asked my provider, and they assured me that the mail was sent to a list with hundreds of addresses on it (including mine). However, only one recipient was shown in Thunderbird, no "undefined recipients" were mentioned. How can I check whether such e-mails were really sent to me in the future?

Thanks in advance!

I've tried the recommended solution for this problem--changing the "security.tls.version,min" from 3 to 1 without luck.

I don't have a problem with Apple Mail on my iPhone.

When I try to access the web version from my Windows machine using Firefox I receive a message "serious security issue with webmail.dca.net. When I try it from a MAC, using Firefox I am able to access mail.

Thanks for any insight you can provide

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My e-mail stopped working a week ago. I get as far as "connecting to IMAP but then get a "Login to server imap.orange.fr with username [redacted]@orange.fr failed" message. I have changed the IMAP and SMTP passwords several times but none seems to work. What am I doing wrong?

Перестали отправляться письма с почтового ящика gmail.com. Соединение с сервером исходящей почты не устанавливается. Разные порты и способы шифрования уже пробовал. помогите решить проблему. Спасибо.