Native S3 support for SES mailboxes.

[ngist]

Amazon SES allows emails to be dumped raw into an S3 bucket. This is currently where I have my RUA and RUF emails setup as it's way cheaper than another gmail mailbox. I noticed that parsedmarc supports writing outputs to s3 but doesn't seem to support reading from S3.

I'd be willing to take a crack at implementing this as a datasource, but I wanted to ask if there'd be any willingness to incorporate the pull requests if I go through the exercise.

It'd require adding at least one config parameter. S3 input_bucket as bucket is already take for output, there should probably also be an output_bucket, and bucket would map to output_bucket to preserve backward compatibility. Maybe some additional options for how the feature would work but haven't thought through those out yet.

Then there's a question of what to do with the blobs that have been parsed. Seems like the easiest thing to do would be move them from an unparsed location to a parsed location similar to how imap emails are archived.

I haven't looked at the code yet but I don't think this is too challenging to implement as the tool can already reads raw emails and parses them, it just need a bit of plumbing to periodically poll S3 for new emails, download them, do what it normally does, and then somehow archive the originals.