How to set an external email address on JSM cloud ?

I would like to set an external email address on JSM. 

However it's a sharing mailbox without password.

I tried to set a mail handler, but it doesn't work. Indeed, I sent an email but not issues have been created.

I am talking about my client email address. It's not a Gmail address and it's not been recognized by Microsoft. 

Someone could help me please ?