Join the Mozilla’s Test Days event from Dec 2–8 to test the new Firefox address bar on Firefox Beta 134 and get a chance to win Mozilla swag vouchers! 🎁

This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

SMTP Timeout error

  • 9 replies
  • 1 has this problem
  • 1 view
  • Last reply by Matt

more options

Hello thunderbird support, please help out: I keep getting this error '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.'

This problem started happening after an update to thunderbird, though this might be coincidental. When I send an email right away it always sends successfully without any issues. I only get the error popup when sending emails that are in the outbox 'send unsent messages' or when I schedule emails using send later.

Here is a list of things that I've tried. I'm using thunderbird on Windows. Email is setup as POP. -I've tried using Windows safe mode, problem still exists -Thunderbird troubleshoot mode, problem still exists -Disabling antivirus, problem still exists (uninstalled the whole antivirus, problem still exists) -Allowed thunderbird in windows firewall, problem still exists -Disabling Windows firewall, problem still exists -Creating a fresh new thunderbird profile under profile manager, problem still exists -Changed from wired to wireless internet, problem still exists -Whether I'm sending fewer emails or many emails, problem still exists -Tried clearing thunderbird: internet cache and cookies using CCleaner, problem still exists -Tried changing all the smtp settings to wrong and then changing them back again, problem still exists -Tried increasing the timeout time mailnews.tcptimeout in Config Editor to 500, and 2000, problem still exists -Tried changing the Connection Settings > Proxy - the 4 different options, makes no difference -Changing the windows clock to a week backwards in time and changing back to correct time

Extra notes: -Creating a new windows local account in Windows on same computer - works no problem! -Using other computers on the same network - works no problem!


I'm totally at my wits end. The username, password, smtp settings, internet connection & settings, computer are all fine. I'll repeat once again the issue, when I send emails immediately it is totally fine every time. When I schedule emails or send from outbox (even a minute later), it comes back with error messages. What is the difference between outbox emails and sending-in-real-time emails that causes this SMTP time out error?

Hello thunderbird support, please help out: I keep getting this error '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.' This problem started happening after an update to thunderbird, though this might be coincidental. When I send an email right away it always sends successfully without any issues. I only get the error popup when sending emails that are in the outbox 'send unsent messages' or when I schedule emails using send later. Here is a list of things that I've tried. I'm using thunderbird on Windows. Email is setup as POP. -I've tried using Windows safe mode, problem still exists -Thunderbird troubleshoot mode, problem still exists -Disabling antivirus, problem still exists (uninstalled the whole antivirus, problem still exists) -Allowed thunderbird in windows firewall, problem still exists -Disabling Windows firewall, problem still exists -Creating a fresh new thunderbird profile under profile manager, problem still exists -Changed from wired to wireless internet, problem still exists -Whether I'm sending fewer emails or many emails, problem still exists -Tried clearing thunderbird: internet cache and cookies using CCleaner, problem still exists -Tried changing all the smtp settings to wrong and then changing them back again, problem still exists -Tried increasing the timeout time mailnews.tcptimeout in Config Editor to 500, and 2000, problem still exists -Tried changing the Connection Settings > Proxy - the 4 different options, makes no difference -Changing the windows clock to a week backwards in time and changing back to correct time Extra notes: -Creating a new windows local account in Windows on same computer - works no problem! -Using other computers on the same network - works no problem! I'm totally at my wits end. The username, password, smtp settings, internet connection & settings, computer are all fine. I'll repeat once again the issue, when I send emails immediately it is totally fine every time. When I schedule emails or send from outbox (even a minute later), it comes back with error messages. What is the difference between outbox emails and sending-in-real-time emails that causes this SMTP time out error?
Attached screenshots

All Replies (9)

more options

You may be successful with this:


   Tap on tools > options > Advanced > General > Config Editor.
   Visit the search file section and put mailnews.tcptimeout > Click Enter.
   Look for mailnews.tcptimeout and right-click on it > modify.
   Here change the value by adding the larger value. Remember to save them.

This appears to be area, but it's all I could find. I hope it works for you. I think the default is 100, so increase incrementally to see if you have success.

more options

Tried that, doesn't solve the problem. Any other idea?

more options

No more ideas. There are a number of entries with word 'timeout' in them in config editor, but I don't know which one(s) may be related. If you don't get any more responses within a day, I suggest you write a bug report on this. https://bugzilla.mozilla.org/home

more options

What happens if you try the Offline setting suggested here:

https://github.com/Extended-Thunder/send-later/issues/396

more options

@sfhowes Thanks for the suggestion, I just tried that but it made no difference, problem still exists.

more options

Perhaps log the send so we can look at the entire action. See what occurred before the timeout.

My Howto: https://thunderbirdtweaks.blogspot.com/2021/10/logging-mail-sending-in-thunderbird.html

Additional Questions. 1. Is the 0365 account a business one (they require oAth loggins is my understanding) or private (Passwords or app poasswords required depending on location in the world)

2.Do you have an antivirus installed to scan outgoing mail? They are so slow that at times they are the cause of timeouts. All on their own. IF Thunderbird is connected to a non saturated network with a fairly bog standard connection to the internet you should not need to look to TCP timeouts except in extreme cases (usually home hackers on their own misconfigured servers)

more options

Thanks for your reply Matt, 1. The O365 account is a business one yes but it was working for 2 years without issues and then a few weeks ago this problem started. It has always been on 'Normal Password' , not 0Auth2. I have tried to change it to 0Auth2 but I get this same problem.

2. I have uninstalled my whole antivirus. I have also disabled the windows firewall.

3. Please see attached photo for the error message in the log.

more options

Other options are: 1) Is there a way to remove that smtp timeout error pop up message?? Because it take overs the entire thunderbird and blocks sending emails that were scheduled for later on, until I manually click "ok" or close the pop up.

2) Is there a windows script that can close that error pop up message whenever it appears whether or not the user is away from keyboard? Like that's all it does.

Because it is precisely the error message that is the annoying thing. When I close that error pop up then it sends out the message like normal. It is the pop up that is causing the entire issue.

more options

lets be clear, there is something very weird going on if the mail sends after the timeout. The message is not the issue and is best ignored until what causes this is determined.

Now do you think you could provide the whole log in text form as I describe in the article. I am not all the interested in the actual error, I am looking for why it is timing out so what was before the timeout is what is missing. I have an idea Microsoft are not sending the completion message,just dropping the connection like a rude uncle at a party. But getting the log is key.