Navigate to Email - Senders in the left menubar. Click the '+ Add' button to add senders. Fill out the details and save the new user. If you want to add extra domains, contact one off our staff members. New domains first need to be verified. Choose whether the sender needs to be linked to an internal user (One Community user) or not. It's possible to create multiple users with the same e-mail and also with the same names but with different signatures. Therefor it's useful to add a description to the sender.
Now that you've created a new sender you can select it while creating a mailing. If you have multiple senders with the same the description will help you selecting the right sender and the right signature.
Choose the option 'Personalized sender' if you want contacts to receive the email from their internal contact person. All contacts without an internal contact person will receive the email from a selected fallback e-mailaddress.