With Sharepoint you can use SP.Utilities.Utility.SendEmail to send email in JavaScript, however you could receive the below error:
“The e-mail message cannot be sent. Make sure the e-mail has a valid recipient.”
After searching the web, I found the solution: instead of using an email address for the recipients you have to use the userDomain with “i:0#.w|”.
For example, if the user is John Doe, and his email is john_doe@company.com, then you should use something like i:0#.w|domain\\john_doe.