Option to disable secondary emails for notifications
Description
Allow administrators to disable setting notifications emails to anything but their primary email address.
Proposal
For those administrators that run GitLab with LDAP as their authentication method it would be nice to have an option that disables users from setting a notification email to something other than their primary (LDAP) email. The reasoning is that if a user leaves the company than you would not want emails going to some personal email they configured.
Yes, you can disable the user in GitLab but in my opinion, the idea behind using LDAP, is you just disable the user in LDAP since that is likely what is being used for SSO in the organization. I don't want to have to disable users twice.
I currently implement this functionality at the SMTP layer. I configure Postfix on the GitLab server to not send email to any untrusted domains. This works well enough but wanted to test peoples temperature on moving this into GitLab itself.
Links / references
N/A