Jenkins email plugin doesn't send email to user who broke the build - email

Question

I've setup Jenkins to send emails only to users who broke the build using email-ext plugin, but I'm getting this error:
Not sending mail to unregistered user user#example.com because your SCM claimed this was associated with a user ID ‘John Smith' which your security realm does not recognize; you may need changes in your SCM plugin
I don't really understand what this error means, is the problem in our SCM, or in the email plugin? The emails are taken from the commit history, should I register them somewhere so Jenkins will start working?
For reference, this is the code around the error message in the plugin's source code:
} catch (UsernameNotFoundException x) {
if (SEND_TO_UNKNOWN_USERS) {
listener.getLogger().printf("Warning: %s is not a recognized user, but sending mail anyway%n", userAddress);
} else {
listener.getLogger().printf("Not sending mail to unregistered user %s because your SCM"
........
How do I enable SEND_TO_UNKNOWN_USERS?
The error message is also mentioned in this bug report.

Answer 1

For version V2.61 or above this can be configured via a radio button.
Go to
Manage Jenkins -> Configure System -> Extended E-mail Notification
and tick the radio button for Allow sending to unregistered users
Edit: If this does not work, see https://stackoverflow.com/a/45353810/492336 for another solution.

Answer 2

OK, after some experiments this is what I found out:
Jenkins takes the email part of the committer (not the author). For example for a commit message that looks like that:
Author: John Smith <author1#example1.com> 2017-07-27 17:15:39
Committer: John Doe <committer1#example2.com> 2017-07-27 17:15:39
Parent: 9c3ff18dda8ca6f7b7ac4ebab4c76d3c85891a33 (commit)
Branch: master
Jenkins will take "committer1", and create a brand new user under People with User ID "committer1" and email "". Unless that user has a password however, it will be considered unregistered so you need to go to Configure for that user and add a password field to it:
So this is one way to fix the error, but you have to do it for every user and in a big team it can be tedious.

Answer 3

Put the line bellow in your jenkins startup script
-Dhudson.tasks.MailSender.SEND_TO_UNKNOWN_USERS=true
The newest Jenkins security directive only allow sending mail to registered user. The line above bypass this configuration.

Answer 4

Given jenkins takes the first part of the email address and creates a user, I made my team have their jenkins user name be the first part of their email address. This removed any overhead of having to maintain two separate users.