Converting incoming emails on the fly with OpenSMTPD filters

This little adventure began with me being annoyed at DMARC aggregate reports. My domain doesn’t have enough email traffic to justify routing DMARC emails to some third-party analytics service, yet I want to take a brief glance at them. And the format of these emails makes that maximally inconvenient: download the attachment, unpack it, look through some (always messy but occasionally not even human-readable) XML code. There had to be a better way.

This could have been a Thunderbird extension, …

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