Service Desk e-mail text truncated by markdown

Summary

Markdown deletes parts of issue text if created via service desk e-mail.

Steps to reproduce

Send an e-mail to a service desk address with this simple body:

foo
*
bar

foo will be in the ticket description, bar will be missing.

What is the expected correct behavior?

The whole e-mail body text should be added to the ticket description.

Relevant logs and/or screenshots

Proposed fix

1. Continue to strip RFC 3676 compliant signatures
2. Anything else, instead of completely removing, embed it in a detail section so that false positives don't erase data (See #3780 (comment 344839022)).