To debug email servers, you may need to quickly send a test email from command line, then check the logs. You can use mail command to send mail. But you need to fill multiple fields.
On Ubuntu/Debian, you need to install mailutils package
apt install -y mailutils
Here is one line command to send email from terminal.
echo "This email body" | mail -s "test email from `hostname`" firstname.lastname@example.org
You can use -v option to verify/debug
echo "This email body" | mail -v -s "test email from `hostname`" email@example.com
Mail Server Solutions
- https://poste.io/ – complete mail server runs in docker. https://poste.io/doc/extending-mailserver