I run a self-hosted mail server for a non-profit student association, where we use aliases on our own domain that forward to users personal email accounts. They

I run a self-hosted mail server for a non-profit student association, where we use aliases on our own domain that forward to users personal email accounts. They configure Gmail to send-as via that alias using SMTP. This has worked very well - users are happy about not having to check multiple email accounts. Sad to see this feature go. Such a short notice, too.