In the settings of the spam folder in your mailbox, you can define which contents are automatically moved to the spam folder or deleted and which contents should not be recognized as spam.

Most email clients allow you to create so-called blacklists and whitelists. In these lists you can explicitly block or allow certain content or senders.

• If certain content and senders are on the whitelist, they are not moved to the spam folder. So if certain emails mistakenly keep ending up in the spam folder, the problem can possibly be fixed by adding them to the whitelist.
• With a blacklist, on the other hand, content that is overlooked by the spam filter is actively placed in the spam folder.

Outlook settings

Settings OWA

Outlook settings:

1. right click on an email in the inbox. -> Click on the menu item Junk Email -> Junk Email Options.

2. remove the checkmark from delete junk emails directly

3. add secure sender -> enter and accept email address

Settings OWA: 

1. Mark, move or delete incoming emails.

2.In the RWTH Mail App (OWA) you can reach the menu item Options under the menu item "Settings".

3.there you can set inbox and cleanup rules. Conditions can be set, such as the occurrence of certain words.

4.Unter der Option “Konten – Blockieren oder zulassen” kann man ebenfalls den Absender blockieren oder erlauben. 

5.under "Block or allow" you can also disable spam detection completely if needed.

IT Center Blog ( RWTH mails in spam folder - why do they end up there and what can you do?)