Blocker Failed to send mails when an email address does not match.
When users have the right to be notified of workflow changes and
to be notified of a new comment they do not receive the mail.
It is possible that it is the case for other right which warns the user by mail
In the code we send a single mail with everyone in copy and if there is a non-compliant email we do not send notifications.
Many ticket at once.
The asynchonous send mail helper takes list of users but send a single mail with everyone in visible copy
We should add an argument to choose if we send separate mails.
In this case, this would solve the issue that is a single mail with lots of people in copy including refused emails