NOTE: This is a copy with formatting fixes of Liron Yahdav's answer that can be chosen as the correct answer. If you want to upvote it, upvote Liron's answer instead.
The solution to this question really doesn't matter what programming language you're using, as long as there's some way to modify Windows registry settings.
Finally, here's the answer:
- To associate a program with the mailto protocol for all users on a computer, change the
HKEY_CLASSES_ROOT\mailto\shell\open\command
Default value to:
"Your program's executable" "%1"
- To associate a program with the mailto protocol for the current user, change the
HKEY_CURRENT_USER\Software\Classes\mailto\shell\open\command
Default value to:
"Your program's executable" "%1"
The %1 will be replaced with the entire mailto URL. For example, given the link:
<a href="mailto:[email protected]">Email me</a>
The following will be executed:
"Your program's executable" "mailto:[email protected]"
Note: The mailto syntax allows for more than just the email address.
Other notes by Liron
@Dillie-O: Your answer put me in the right direction (I should have expected it to just be a registry change) and I got this working. But I'm going to mark this as the answer because I'm going to put some additional information that I found while working on this.