Should we consider checking email address validity before handing email on?

[stevejalim]

Configurable option to reject emails where the from-address does not match an email-address regex (it'd have to include unicode chars). This would prevent email from deliberately fake senders (or accidentally misconfigured clients) making it into the project's data stores

This could be added to every backend, or everywhere via a base, perhaps

[hugorodgerbrown]

Great idea, should be implemented as part of this issue - #17