The GMX spam filtering functions detect unsolicited e-mail and move them to the Spam folder. You can move spam e-mail that were not detected to the Spam folder by clicking Spam. That trains your personal spam filter, which will then always classify any future e-mail from the sender and e-mail with a similar text pattern as spam.
Conversely, in rare cases, an e-mail you want to receive may be classified as spam. Click Not Spam to move this e-mail back to the Inbox folder. Your personal spam filter will then no longer classify future e-mail from this sender and e-mail with a similar text pattern as spam.
If a Spam message contains external content, it will not be shown. This is to prevent the spammer from seeing that the message was read. If you still want to view the content, click on Show all.