PLT-2719 Emails with underscores don't auto-link correctly (#2865)

tests/test-links.md

@@ -67,3 +67,4 @@ https://en.wikipedia.org/wiki/URLs#Syntax links to the Syntax section of the Wik
 test@example.com links to `mailto:test@example.com`  
 [email link](mailto:test@example.com) links to `mailto:test@example.com` and not `http://mailto:test@example.com`  
 [other link](ts3server://example.com) links to `ts3server://example.com` and not `http://ts3server://example.com`  
+test_underscore@example.com links to `mailto:test_underscore@example.com`