The specification for 'mailto' body says:
The body of a message is simply lines of US-ASCII characters. The
only two limitations on the body are as follows:
- CR and LF MUST only occur together as CRLF; they MUST NOT appear independently in the body.
- Lines of characters in the body MUST be limited to 998 characters, and SHOULD be limited to 78 characters, excluding the CRLF.
https://tools.ietf.org/html/rfc5322#section-2.3
Generally nowadays most email clients are good at autolinking, but not all do, due to security concerns. You can likely find some work-arounds, but it won't necessarily work universally.