Guess no one asked me this before and I didn’t run into this question yet. However, today I got approached with the question how line breaks can be entered in a mailto: command.
The answer can be found in RFC 2368 whereas line breaks in the body of a message must be encoded using the %0D%0A sequence, which in case is nothing else then hexadecimal for 10 (line feed) and 13 (carriage return).
A full mailto: command using this feature could look like this:
mailto:firstname.lastname@example.org_t?subject=Header&body=This is the first line%0D%0AThis is the second
Strictly speaking should the white spaces also be replaced with the appropriate ASCII code which is %20 and makes the complete command to look like this: