What the upgrade involved

Two known issues stand. Equal-preference MX records are not randomised (RFC 5321 5.1); the server always tries them in the order the resolver returned, and a comment and COM help string that claimed otherwise have been corrected. One-click unsubscribe (RFC 8058) is not implemented. RFC 2369 List-* headers are still emitted for distribution-list postings.

Changes

• Postfix pipelines the terminating dot and QUIT into one segment, so the terminator sits mid-buffer and every tail-only end-of-data check missed it. The receive path now searches for <CRLF>.<CRLF> anywhere in what arrived and returns the remainder to the command parser. Bare-LF terminators are still recognised only at the very end of the buffer, with anything behind them discarded, which is the CVE-2023-51764 rule.
• SMTP dot transparency (RFC 5321 4.5.2) now carries line-start context across buffer boundaries in both directions. Previously a line-leading dot landing a byte or two into a chunk went unstuffed, silently truncating messages.
• Sieve scripts were left behind by domain and account renames and deletes. Recreating an address could reactivate the previous holder's filter, redirects included. Renames now move the Sieve tree, deletes remove it, and the Control Panel writes the script only after the save succeeds.
• Sieve body test (RFC 5173) implemented and advertised over ManageSieve, with :text, :content and :raw.
• SORT () US-ASCII ALL spun a connection thread at 100% of a core forever. Empty sort criteria are now rejected per RFC 5256.
• The 512 MB message-list cache never evicted and only counted upwards. Eviction now measures entries as they are.
• Malformed DNS answers are retried once over TCP. The Control Panel MX tool (#29) now uses the server's resolver via Utilities.ResolveMXRecords.
• Control Panel: seven Administrator functions restored, plus Welcome page icon alignment (#30).

Everything in the 6.2.20 notes is in this release too.

Full release notes, checksums and signatures