This error occurs when the SMTP server blocks the messages. This may also happen when sending messages is blocked by ISP restrictions to outgoing ports and mark them as spam. To send and receive emails SMTP is used as an internet standard by the users.

Regards, Will

Will, Thank you for responding. I am not sure what to do with this information. As I said in my original post, it happened, abruptly, Tuesday night (20 June 2023). I have not changed any settings in Thunderbird since I installed it months ago. Plus, my iMac, iPhone, and iPad Pro are sending and receiving emails perfectly, as they have been doing for several years.

It is only Thunderbird on my Windows 10 PC that is having a problem sending emails. My internet/email provider, Spectrum (Charter Communications) verified they had not made any changes to the email server that would have affected my ability to send emails.

Since my Apple computer and mobile devices are unaffected and still handle send/receive emails as always, it comes down to either my provider, Spectrum, or Thunderbird. I find it strange that all of a sudden, Thunderbird can not send email.

I still do not know what I need to do to correct this problem.

Thank you,

Randy

re :He had me login to my email account via the Spectrum Webmail link. That merely proved you knew your password and proved from Spectrums point of view that you had another means of viewing/sendng emails. It's not relevant to Thunderbird because Thunderbird uses imap, pop and smtp protocols.

But you are the second person within a few hours to mention this inability to send via spectrum servers.

Please check the server smtp settings.

You mention charter so are you using these settings:

SMTP

• Description: full email address - same as User name.
• Server name : mobile.charter.net
• Port: 587
• Connection Security: STARTTLS
• Authentication Method: Normal Password
• User Name: full email address

click on OK

Then Exit Thunderbird wait a few moments for background processes to complete and start Thunderbird.

Toad-Hall,

You are correct. I am using the settings you listed: SMTP

Description: full email address - same as User name. Server name : mobile.charter.net Port: 587 Connection Security: STARTTLS Authentication Method: Normal Password User Name: full email address click on OK

But that was always the settings and was still the setting when Thunderbird suddenly stopped sending emails. Nothing with Thunderbird settings had changed. On Tuesday night, I tried to send and email and Thunderbird ask me to enter my password. So, entered my password and the email would not send, got a message that the email would not send as the SMTP server mobile.charter.net had timed out.

That is how it all started and I can not get Thunderbird to send emails.

I double checked my SMTP settings to verify nothing had changed. I then deleted Saved Passwords, just in case for some reason the password file had been corrupted. Still keeps asking me to enter my password at startup and when I attempt to send an email.

I do not know what else to do. I am going to call Spectrum tech support again.

Thank you,

Randy

I am having this problem too (incoming works but sending mail fails), but I use Shaw in Canada (shaw.ca). After calling them they did the same thing--confirmed that I could send and receive from the web based Shaw and then told me it was not their fault, but a problem with Thunderbird. They don't have settings listed on their site that I can find.

I am using Thunderbird 60.9.1

I have been reluctant to update it, because things tend to break and if it ain't broke..... But I am willing to entertain that advice if it is necessary.

All my settings for POP and SMTP are the same as they always were. I have tried the following:

1. Disabled my VPN Firewall Antivirus

2. I have run a system check at the command line

sfc /scannow

and no problems found.

3. I have restored by profile.ini and profile folders from a backup

4. I have tried restarting in safe mode (with add-ons disabled).

5. In Account settings I have tried changing the ports retyping the server name, change connection security to none changing authentication method to no authentication

Nothing seems to work. I get a few different error messages:

1. An error occurred while sending mail. The mail server responded: <xxxemailaddress@shaw.ca> sender rejected. Please verify that your email address is correct in your account settings and try again.

2. Sending of the message failed. An error occurred while sending mail: Outgoing server (SMTP) mail.shaw.ca is unknown. The server may be incorrectly configured. Please verify that your Outgoing server (SMTP) settings are correct and try again.

3. Sending of the message failed. The message could not be sent using Outgoing server (SMTP) mail.shaw.ca for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again.

I have considered deleting my account and rebuilding it but that seems a bit scary.

I could paste relevant troubleshooting information here if anyone can look through it and try to help me.

I am very grateful for any help you can suggest.

Thank you.

L.