Email attachment

How it works

RFC 2045 defines the packaging. Base64 adds about a third to the wire size. Gateways scan and sometimes rewrite the part. A link in the body is not an attachment. It is a pointer.

A 6 MB PDF attaches and arrives. The hash differs because a gateway added a footer. They switch contract delivery to a link so the hash stays stable. The mail remains the notice.

How it differs

An attachment is a push into a mailbox. A file request is a pull onto your server.

Mail stores the file in every recipient mailbox. That is extra copies.

Prefer a link when the file is sensitive or large.

On the ticket

• The practical close is a log line: time, actor, byte count, result.
• Without that line the transfer is a story.
• With it, the next person can see whether this door did what the ticket claimed.
• If the path is shared, say so in the partner profile so a later change does not silently pick a different limit, key, or region.
• On a real ticket, write down the door, the byte count, and the clock.
• For email attachment, that means naming the host or bucket, the expected size, and the time the other side must have a complete file.
• A progress bar is not that record.
• A 200 response that arrives before the complete call is not that record.
• If a retry is allowed, say how many and whether it resumes.
• If a person must approve the send, name the person.
• Partners who receive email attachment files should match on hash or size before they import.
• A same-length corrupt file passes a size check and fails a hash.
• Keep the published hash off the only channel an attacker can edit, or treat it as a corruption check rather than a substitution check.
• When the path changes, new key, new region, new cap, update the profile the same day so the next run does not use a stale limit.