Works great but some features are missing

Thank you @markus0815 for your feedback.

@kofimokome thank you very much for the fast update reflecting my wishes (link filter / custom error message)!

The link filter detects currently all occurrences of https which could lead to false positives, since we use the mail form for software support.

I would like to propose using a regex:
https://stackoverflow.com/questions/6038061/regular-expression-to-find-urls-within-a-string

Ideally it would detect urls starting with https://, https://, fto:// but also urls where the protocol is omitted.

ok. I will look at it.