Teams channel email delivery fails for non-team member

I'm logging this, and the solution because I found LOTS of similar problems due to the first line of the email returned to the sender being a generic Microsoft sentence used in lots of email bounce backs.

Setup

We have a TEAMS team , that has 4 members, we published the email address for that channel to the company using an Exchange Contact (so we could change it later if required).

The goal being anyone in the company could email the channel, so the teams team members would ALL have visibility to the emailed material.

The problem

A staff member emailed the Teams Channel email address and got a reply which stated the following:
Subject: Undeliverable: Test submission

Body of email: 

Delivery has failed to these recipients or groups:

email address removed for privacy reasons
The sender is not a member of the team and does not have permission to send email to this channel.

Searching for the delivery has failed, gives back LOTS of google relsults that aren't the issue because that first line in the email is used for lots of errors.

So I looked at the email headers and that didn't help me much.

THE KEY is searching for the third line in the bounce back email  "the sender is not...."

Turns out that every TEAMS channel email address now has "Advanced Options" , which didn't used to be there (I don't know when this was implemented)
https://support.microsoft.com/en-gb/office/manage-who-can-send-email-to-a-channel-in-microsoft-teams-4f1a1224-e71b-45de-8f68-8e08f7874fa9#:~:text=%3E%20Get%20email%20address%2C%20and%20then,your%20audience%20to%20specific%20domains

It seems the default (please reply if you know for sure) is the "only members of this team" can send to this channel.

Solution

If you're getting users reporting they can't email a TEAMS channel and the email they get back contains "The sender is not a member of the team and does not have permission to send email to this channel." the fix is simple: change the channel's email advanced settings 🙂