Hi @Juul van de Wal
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to accept the answer.
sol
I've received a simple solution.
When opening the teamschannel > click on 3 dots > click on 'Get email address' > open 'Advanced settings' > select the option 'Anyone can send emails to this address.
The above was not visible for members of the teams. So I first needed to become an 'Owner' of the teamschannel.
If the answer is helpful, please click Accept Answer and kindly upvote it so that other people who faces similar issue may get benefitted from it.