It might be that you receive the message
You are not allowed to post to this mailing list, and your message has been automatically rejected. If you think that your messages are being rejected in error, contact the mailing list owner at firstname.lastname@example.org.
when you try to post a question to the email discussion list. The most frequent cause for rejecting messages is that the email address from which you are sending the email is different from the one that you used to subscribe to the email list.
For example, you might use email@example.com to send messages, and firstname.lastname@example.org to receive them. On your side it might appear that both email addresses are the same and messages to both might end up at the same location on your computer, but to the email list server they are different.
To ensure that your email reaches the email discussion list, you have to ensure that the address configured in your email client as the “from” address is the same as the one you used to register. So the solution is to register with the same address as the one you have in your “from” field.
Alternatively, you can also register with both addresses and then use the web interface to configure one of the email addresses not to receive emails. That allows you to send from both, but you won't be receiving messages twice.