Import upstream v0.16.22, stripped

Upstream commit: 474dd0229cb20cf513036619781ed97bd8073c3f
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 117 in 50 files
Dangling module declarations removed: 5
Cargo edits turning enterprise off: 14
Verification: clean
Enterprise feature gates left for rebuilt features: 19 in 18 files

Produced by tools/fork/strip.py. The full report is in docs/fork/strip-reports/ on main.

tests/resources/smtp/dsn/failure.eml

@@ -0,0 +1,48 @@
+From: "Mail Delivery Subsystem" <[email protected]>
+To: [email protected]
+Auto-Submitted: auto-generated
+Subject: Failed to deliver message
+MIME-Version: 1.0
+Content-Type: multipart/report; report-type="delivery-status";
+ boundary="mime_boundary"
+
+
+--mime_boundary
+Content-Type: text/plain; charset="utf-8"
+Content-Transfer-Encoding: quoted-printable
+
+Your message could not be delivered to the following recipients:
+
+<[email protected]> (host 'mx.example.org' rejected command 'RCPT TO:<foob=
+[email protected]>' with code 550 (5.1.2) 'User does not exist')
+
+
+--mime_boundary
+Content-Type: message/delivery-status; charset="utf-8"
+Content-Transfer-Encoding: 7bit
+
+Reporting-MTA: dns;mx.example.org
+Arrival-Date: <date goes here>
+
+Final-Recipient: rfc822;[email protected]
+Action: failed
+Status: 5.1.2
+Diagnostic-Code: smtp;550 User does not exist
+Remote-MTA: dns;mx.example.org
+
+
+--mime_boundary
+Content-Type: message/rfc822; charset="utf-8"
+Content-Transfer-Encoding: 7bit
+
+Disclose-recipients: prohibited
+From: Message Router Submission Agent <[email protected]>
+Subject: Status of: Re: Battery current sense
+To: [email protected]
+Message-id: <[email protected]>
+MIME-version: 1.0
+Content-Type: text/plain
+
+
+--mime_boundary--
+