Thunderbird Community Forum

I am assisting an elderly user with a personal @hotmail.com account that receives email successfully in Thunderbird but cannot send. I have confirmed they can send and receive emails from their online outlook.com portal. The user's computer setup is as follows:

• Windows 11 (with latest updates).
• Thunderbird 153.0.2 (64-bit).
• A personal @hotmail.com account with the following server configurations:

  -> Incoming IMAP: outlook.office365.com, port 993, SSL/TLS, OAuth2, and
  -> Outgoing SMTP: smtp-mail.outlook.com, port 587, STARTTLS, OAuth2.

Thunderbird successfully authenticates to Microsoft using OAuth2 for incoming email. However, when Thunderbird attempts outgoing email authentication, Microsoft's SMTP server rejects the authentication. The Error Console in Thunderbird records this message: "535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox."

-> Refer to attached image: "Thunderbird Error Console_20260811.jpg". -> I am able to provide a short screen recording demonstrating the failure if needed.

To try and resolve the above, I completed the following actions:

1. Confirmed Thunderbird is current (153.0.2).
2. Confirmed SMTP is configured for OAuth2 rather than Normal Password.
3. Confirmed port 587 and STARTTLS.
4. Re-authorised the Microsoft account/OAuth connection.
5. Confirmed IMAP OAuth2 works.
6. Confirmed Outlook.com webmail can send successfully.
7. Reviewed Mozilla's current “Microsoft OAuth Authentication and Thunderbird in 2026” guidance, including the section covering cases where IMAP/POP works but SMTP does not.
8. Captured the SMTP failure in Thunderbird's Error Console.

However nothing worked, so I raised the matter with Microsoft support and eventually had the matter referred to their Tier 2 team. The Microsoft case number is: 7107041963.

Microsoft Support confirmed that for a personal Outlook.com/Hotmail account there is no user-accessible mailbox-level SMTP AUTH setting, and advised that SMTP is enabled by default for supported clients. However, because sending from Outlook.com webmail works, Microsoft Tier 2 declined to investigate the SMTP server response further and directed me to Thunderbird support.

I am able to provide a copy of the chat transcript if needed.

In any event, the TLDR version IMAP works using OAuth2, but SMTP using OAuth2 fails because Microsoft's SMTP server reports SmtpClientAuthentication is disabled for the Mailbox. Microsoft Tier 2 has referred the issue to Thunderbird support.

Questions:

1. Is this a known current issue affecting personal Outlook.com/Hotmail accounts using Thunderbird?
2. Is 535 5.7.139 SmtpClientAuthentication is disabled for the Mailbox known to occur with Thunderbird OAuth2 even though IMAP OAuth2 succeeds?
3. Is there a current Thunderbird-side workaround or alternative SMTP server/configuration recommended for personal Hotmail accounts?
4. Would changing the SMTP server from smtp-mail.outlook.com to smtp.office365.com be appropriate for a personal Hotmail account in Thunderbird 153, or should the current Microsoft-documented server be retained?

-> I note there appears to be conflicting advice on this point in previous support threads.

1. Given that IMAP OAuth2 authentication succeeds for the same Microsoft account, does this indicate that Thunderbird's Microsoft OAuth authorisation itself is functioning correctly, or could SMTP require a separate permission/token that may be failing?
2. Are there any additional Thunderbird logs or diagnostics I can provide that would help resolve this matter?

Disclosure: I used ChatGPT to help organise my troubleshooting notes and technical details for this post. The troubleshooting, observations and diagnostic information described above are from my own work on the affected PC.

Im looking for help to set up my Hotmail account. I have 4 emails. They all worked perfectly for a long time. All of a sudden, everything just stopped. I have tried everything and the configuration seems to be correct. Ive tried every fix i could find. It just no longer makes sense to me. Does it just not work with Thunderbird? The specific message is "User is authenticated but not connected". Also when i tried to send an email, i get "Login to server smtp-mail.outlook.com with username **********@hotmail.com failed."

I have installed Thunderbird to work with my spectrum email account. I had successfully installed it and was even able to recieve emails, but could not sent them. I uninstalled it, reinstalled it and now I can't receive emaill either. The settings for the servers and my username (fulll email address) all look correct per spectrum's website. Whenever I enter my password into Thunderbird I get:

"Login to server mobile.charter.net with username stynee@ca.rr.com failed."

Next steps?

Hi, I have two accounts in my Thunderbird. They are Gmail (regular gmail account) and CFCC (an institutional account). The CFCC shows up in my Unified Folder list but the Gmail does not. Is that normal? The main Inbox is showing all incoming emails from both accounts so no performance issues, just wondering how to get rid of the CFCC (if that's possible) to eliminate clutter. Thank you. GES

My folders are in disarray and it is cutting into my productivity to file emails. I have tried but it in settings but it doesn't work. Many are in alpha order but there are 2 different two different sections of the same name, and some odd files end up in an alphabetized section.

For instance there are 2 different ZBV sections with other stray folders in the same area that should be in there own alpha folder area. It's a mess to find the right folder. I have to scroll up and own and look for the folder I need to file in. I would be happy to donate, and i have in the past, but I really need this to get fixed. Please, please, please...

It seems it is because BUGZILLA uses the AMAZON'S service, but there is now a RANGE of IP addresses that have been blocked, and BUGZILLA have been caught up in this mess. Please let me know which board I can use to report/ask about this issue, if it is no on here..

Here is the issue research (NOTE: I have emailed the BMO_MODS email several times, but had NO RESPONSE, so want to check if others have this issue):

Based on the error message you're receiving, Microsoft is blocking emails from your IP address because it appears on their block list. This is a Microsoft-specific issue rather than an AWS problem. When you receive a 550 5.7.1 error with the S3150 code from Microsoft domains (Hotmail, Outlook), it means Microsoft's filtering systems have identified your IP address as a source of problematic traffic. Even though you're using a managed dedicated IP and haven't intentionally violated any policies, there are several reasons this could occur: The IP address may have a poor reputation due to previous usage by another customer, spam complaints from recipients, high bounce rates, or sending patterns that Microsoft's algorithms flag as suspicious. Sometimes legitimate senders get caught in these filters. To resolve this issue, you should:

• Contact Microsoft directly using the troubleshooting link provided in the error message (mail.live.com/mail/troubleshooting.aspx) to request delisting
• Review your email sending practices to ensure you're following best practices (proper authentication, low complaint rates, engaged recipient lists)
• Consider contacting AWS Support to discuss your dedicated IP's reputation and whether a new IP might be warranted
• Ensure your SPF, DKIM, and DMARC records are properly configured Microsoft maintains their own independent block lists and reputation systems, so even with AWS's managed infrastructure, you may need to work directly with Microsoft to resolve deliverability issues to their domains.

Account Settings > + Add Account > Mail Account > filled in Full Name and gmail e-mail address in Mozilla Thunderbird Account Hub > Continue > Account settings found automatically > Continue > Connect your e-mail settings "Waiting for authorization in login popup..." > website appears on my Brave web browser > Mozilla Thunderbird Email wants access to your Google Account > Select what Mozilla Thunderbird Email can access > Select all > Continue > error appears "This site can’t be reached localhost refused to connect. Try:

Checking the connection Checking the proxy and the firewall ERR_CONNECTION_REFUSED" > Mozilla Thunderbird Account Hub, Connect your e-mail settings page says Waiting for authorization in login popup with spinning circle still there. Any simple, step by step, instructions to get my gmail account added to Thunderbird would be much appreciated. Thank you for your attention to this matter.

Hello,

The new August 10 release tags every message in red when it's clicked on.

Now the messages I DID tag don't stand out because they're all red. I cannot find anything in Manage Tags to undo it tagging every message to no avail.

How do I stop every message from being tagged red on its own?

Thanks, Theresa

There was an earlier Case with the exact same name as what I named this case which was archived back in 2025. I have been living with this same problem since last year also. In the previous case there was reference to "downgrading" to an earlier version of TB, but there have been a bunch of updates since then so I doubt that would fix my problem because that earlier version is now over a year old.

I have one Gmail folder that correctly has one folder label "Junk." However, I have 4 folders that are AT&T related (2 from the domain "sbcglobal.net" and 2 from the "att.net.") For some reason when I set these folders up years ago they started out as labeled "Spam" instead of "Junk." Of those 4 folders 2 of them have the duplicated "Spam" folders, one from each domain."

When I go to Folder Properties I see "imap://XXXXX%40sbcglobal.net@imap.mail.att.net/Junk" on one of these Spam folders and "imap://XXXXX%40sbcglobal.net@imap.mail.att.net/Bulk" in the other. And the same "Bulk" vs "Junk" issue is in the other domain as well. All are named "Spam."

Can I simply delete one of these folders that are named "Spam" in each domain? Does it matter whether I delete the one ending in "Junk" or the one ending in "Bulk?"

Thanks.

just got Thunderbird, i added my outlook email then got to the "connect your email setting" then i clicked continue cause i wanted to use imap and got a "Authentication error". I got Thunderbird on a different device and used my gmail on that device and it worked fine. Only get the error when i try to use my outlook email and i don't know what to do.

Hello Thunderbird Support, I am experiencing a severe IMAP folder synchronization loop with my Yahoo Mail account (paulpersonne519@yahoo.fr) inside Thunderbird. Yahoo Support claims the issue is caused by Thunderbird's folder mapping, so I am reaching out to you for a solution.

1. 1. The Problem:

The system-protected folder "Bulk" (Spam) has somehow been moved or mapped as a subfolder inside the "Trash" folder.

• In the Yahoo Mail Web UI (Chrome), the subfolder is invisible, but the Trash directory shows an arrow (^) indicating a child folder exists.
• In Thunderbird, the Bulk folder is clearly visible inside the Trash folder, marked with the flame (Junk) icon.

1. 1. What goes wrong:

When I delete spam messages via Thunderbird, they get trapped inside this nested Trash/Bulk directory. If I try to delete or empty it, the emails disappear but the folder itself cannot be removed.

1. 1. Steps tried so far that failed:

  1. Attempting to delete or rename the Bulk folder inside Trash gives the server error: [CANNOT] DELETE failed - Mailbox is reserved.
  2. Using Shift + Delete on the folder is rejected by the Yahoo server.
  3. Unsubscribing from the folder via "Advanced IMAP settings" -> "Show only subscribed folders" fails; Thunderbird re-downloads the structure on the next sync.
  4. I have completely deleted my old Thunderbird profile folder and created a brand new one using thunderbird.exe -P. Upon adding the Yahoo account via OAuth2, Thunderbird immediately pulled the same broken Trash/Bulk structure from the server again.

Since Yahoo refuses to help and claims Thunderbird caused this mapping loop, is there a hidden config setting (about:config) or a database override in Thunderbird that can force the server to release or move this reserved folder back to the root directory? Thank you for your assistance.

Hi.

Just had a not requested update to 153 esr, which in itself is generally fine, with a small exception.

The windows min, max and close buttons all come up with a code.

Probably just some weird setup I have but any ideas will be welcome.

I use userChrome.css to give a background colour, so maybe the ID of each has changes for any css

1. titlebar-min{height:1.66em; background:#00b !important}
2. titlebar-max{height:1.66em; background:#090 !important}
3. titlebar-close{height:1.66em; background:#d00 !important}

but I don't see how that would effect the actual bare icon

Thank you

I am in the midst of the long process of moving most (not all!) of my gmail from the gmail server to TBird, using filters as discussed in this thread.

I've started by first using filters on less important emails (ie so that no true disaster occurs if something goes horribly wrong). As I do so, I have questions!

For example, let's say I use a filter to: copy all the emails from @someone.org to a local folder then delete those emails (from the server)

What happens if one of those emails happens to be within a thread, including emails from people who don't match the filter (ie are not @someone.org). Have I broken the thread forever, ie, has something gone horribly wrong? If so, how do I prevent this behavior/have the entire thread move along with the targeted value? If not, I don't see how I can move email without breaking threads, which is a bit of a problem.

(Also - whoops, I see I should update, but the question remains.)

Thunderbird has stopped downloading mail from the outlook account for my prime account, but my secondary account also outlook is OK. It kept asking to sign into my account then directed me to a web page to sign in for outlook, but it would only let sign into the 2nd account. I have tried uninstalling Thunderbird and re-installed it but still have the same problem.

Greetings,

I just downloaded Thunderbird onto my new laptop. I use AOL as my mail server (not voluntarily; they own the verizon.net email domain). This is also my 1st foray into IMAP.

On Thunderbird, there are two "Drafts" folders (identical spelling). My draft emails go to one of the two. I cannot unsubscribe from either by using the any of the methods I found on here (including: uncheck, close Subsribe, close the program, wait a few mins, then open the program). The result is that both "Drafts" folder remain on the LH panel and both remain checked in the Subscribe window.

An interesting note is that the properties of the "Drafts" folder that does not receive draft emails is: "imap://w5mt%40verizon.net@imap.aol.com/Draft" with the Name in the Folder Properties window as "Drafts" (this cannot be changed in the Folder Properties window). The properties of the "Drafts" folder that does receive draft emails is: "imap://w5mt%40verizon.net@imap.aol.com/Drafts" with the same Name, "Drafts".

Just to make things more entertaining, AOL Mail also has two "Drafts" folders; one is in the list of folders below Inbox and does not receive draft emails, the other is in the Hidden Folder List and that is where draft emails go. The "Draft" in the main folder list can't be manipulated (e.g. moved). The one in the Hidden Folder List can't be moved to anywhere outside the Hiden Folder List.

In Thunderbird, I would just like the "unused, undesired" "Drafts" folder to either be deleted or hidden. At present, neither option seems possible.

Thoughts appreciated.

Thanks Matt T

Incoming mail on my windows 11 computer has begun appearing in the Sent folder instead of the Inbox. It appears to have started 7/26/26. When I right click on the message I see an option to "move to inbox again".

  This does not happen on my Macbook.