E-mail sent from tutanota may be getting caught in spam filter


New Email
When I send an e-mail from my tutanota account to my friend at his work e-mail account, he does not receive the e-mail. He thinks the spam filter at his work is blocking it. I told him to send me an e-mail at my tutanota account and to add my tutanota address to his address book. Is there something else that I should do?