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?
Maybe it's using a reputation and/or RBL service that still gives the @Tutanota a poor score.
It might help if your friend can help provide some details here too such as any spam scoring and other info recorded in the full email headers on their end.