Give access to outsiders for an internal shared Mailbox

Let's imagine you have a few Shared Mailboxes on your company, and you want people from outside the company to have access to them, how do you do that?

As you probably know, Microsoft only allows the delegation of Shared Mailboxes to accounts that belong to the domain the shared mailbox is also in

1) Invite an external user, but on the next window, when you have to specify the user type, ensure you set the user as a "member", then invite the user

2) Edit the properties of the new account, adn ensure the domain is set to designmuej.org

3) they logn using the 

References

• https://www.cloudficient.com/blog/everything-you-need-to-know-about-shared-mailboxes-in-office-365 
• https://learn.microsoft.com/en-us/microsoft-365/admin/create-groups/create-groups?view=o365-worldwide