Hello there philfrae we have read your message we try to help you.

you are using a mobile device or laptop or a device like a iphone.

The error codes . Incorrect mail settings. Or filled in incorrect mail server name. wrong password or a bug.

Trying to fix this is in following subjects. check the usser-account his username.

email account password have to be checked. see for the incoming mails and outgoing mail traffic if there is a wrong configuration.

your Smtp settings also has to cheked if they are oke? Configurations with the filled innumbers for the port numbers ,also.

i will send you these forms to help you with these steps.

https://support.mozilla.org/en-US/kb/cannot-send-messages#:~:text=Verify%20that%20your%20outgoing%20email%20is%20not%20being%20blocked%20by,and%20sending%20another%20test%20email.

https://support.mozilla.org/en-US/kb/cannot-receive-messages

https://support.mozilla.org/en-US/kb/automatic-account-configuration

greetings firefox volunteer.

Hi, thanks for your reply. I have done all the things you suggested with no luck. Thunderbird is up to date and is running on a Mac with OS Catalina. I can receive emails, the only problem is sending. I have set up a new email address with the email provider and that works perfectly, send and receive. I have deleted the old email address in Thunderbird, created it again manually, and I still can't send. I have opened the error console and I attach a screenshot when the send failure occurs. Regards Phil

Thunderbird is not rejecting anything. Either the server you are using to send is rejecting the message or the receiving server is rejecting the email.

Info says Command failed : 550 Message Rejected (104)

Typically this is a standard type of response when a server spam filter has blocked the message.

You could check with spamhaus to see if your IP address or domain have been blacklisted. https://check.spamhaus.org/

Or whether the type of email you are sending shows typical signs of a spam email eg: loads of links or images.

You would need to provide info to see if this is due to you trying to send via eg: an insecure port etc In Thunderbird Menu icon > Help > More TRoubleshooting Information Under 'Mail and News Accounts' Copy all info and paste into this forum question. state the number of the account with problem.

You could also determine if your email address is blacklisted, check your email domain (the part of your email address after the @ symbol) using MXToolbox.

• https://mxtoolbox.com/blacklists.aspx

MXToolbox will check your email domain against over 100 blacklists.