Thunderbird receives emails, but I can’t send any?

If you are experiencing problems with receiving or sending emails in your email client (e.g. Thunderbird), please check the server settings again first, especially those of the outbox server. Here you can find the necessary information.

If problems still occur, this may be caused by installed antivirus programs or the firewall.
To check this, you can temporarily deactivate the antivirus program. If the sending process then works, the manufacturer can normally provide information on how to add exception rules for the email client.

The same procedure can be followed with the firewall. Here are the commands for the most common operating systems. If the firewall turns out to be the culprit, exception rules can be added to the firewall.

Ubuntu, Debian

sudo systemctl stop ufw

To see whether the firewall is active or not, use the following command.

sudo ufw status systemctl status firewalld

Fedora, CentOS

sudo systemctl stop firewalld

To see whether the firewall is active or not, use the following command.

sudo systemctl status firewalld

Windows: Official Windows Support

MacOS: Official Apple Support