PDF is always attached when messages are sent by e-mail (Transmission Medium 7: Simple Mail) NAST

PDF is always attached when messages are sent by e-mail (Transmission Medium 7: Simple Mail) . How can I suppress this?

In Detail:

I send an email from order processing with the standard message MAIL

The RSNASTSO program with the form Routine SAPOFFICE_AUFRUF_VX is stored in Customizing for output type MAIL. So also standard.

A PDF is always attached to the email I receive. The PDF contains the mail text stored in the message type.

Result in Outlook:

Even if I remove the mail text in the message type in Customizing, an empty superfluous PDF is still attached.

How can I prevent this PDF from being attached?

I have already copied the RSNASTSO program to ZRSNASTSO and made various changes. Unfortunately without success. Or is this a general customizing setting?

Thank you for reading