Reply to user if email processing fails - Githubissues

aksiksi / vaulty

A service that allows users to send email directly to a cloud storage service.

https://vaulty.net

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Reply to user if email processing fails #48

Closed aksiksi closed 4 years ago

aksiksi commented 4 years ago

Instead of relying on bounces, we can respond to the user if processing fails for a particular email.

The idea is to use In-Reply-To header to specify which Message-ID we are responding to. This enables threading in the user's mail client. See this for further details.

Tools

lettre: mail sending library
lettre_email: mail builder library, supports setting the headers mentioned above
tokio spawn_blocking: allows the filter to spawn blocking tasks. might not be needed.

Notes

Apparently, Gmail uses the Subject and In-Reply-To headers to thread messages. In other words, you cannot change the original message subject.