Mail in the spam box

[Red_Butler]

An internet connection of mine, who doesn't know very much about computers has the following problem.

If I send him an email, it always lands in the spam box. He says he tried to change some things, but my mails keep landing there.
I tried out what caused it and it seems to happen only if I send my mails in html.
Only if I send mails in plain text it lands in his mail box.

He is using a gmx account and he doesn't use an email program to download it to his computer. He just signs in at gmx.

My question is: does anybody know what he should do to get my mails in his mail box?
I prefer a solution described in german, because he has a german account and he doesn't understand english.

Red Butler

 

[Smade1]

Ask him to add your address to his address list.