If you tried to install 6.2.19 on a fresh machine and it failed or hung, this release is the fix. Upgrades from existing installations were never affected. Everything in the 6.2.19 notes is in this release too.
The fresh-install failure in 6.2.19

Two defects stacked, and each is worth a sentence because each is a class.

The database creation failed. The SQL script runner splits a script into
commands on blank lines, and SQL Server Compact — the embedded database a fresh
install uses — executes one statement per command and refuses a batch. A recent
change added settings to the create scripts with a single newline between
inserts: three statements, one command. Full SQL Server accepts that batch, so
the development database and the 1,490-test regression suite saw nothing wrong;
only a fresh install runs the create script against SQL CE. The same adjacency
was in the MySQL script (whose client refuses multi-statements by default too)
and the PostgreSQL script. All three are fixed, and a mechanical sweep of all 199
SQL scripts confirms no multi-statement command remains in any create script
or any SQL CE script. (Five upgrade scripts from the hMailServer 5.x era carry
batches for the full-server backends that accept them; they have a decade of
successful upgrades behind them and are deliberately left untouched.)

The failure hung instead of failing. The error raised a plain message box,
and /VERYSILENT /SUPPRESSMSGBOXES suppresses only the suppressible kind — so
a silent install did not report the failure, it waited on a dialog with nobody
at the keyboard. In CI that was ninety minutes until a person cancelled it; on a
real unattended deployment it would have been forever. Every dialog in the
installer (28 of them — any one was a potential silent-install hang) now takes
its default button under /SUPPRESSMSGBOXES, and the installer proceeds to an
exit code a deployment script can actually read. Interactive installs see
exactly the dialogs they always saw.

Who was affected: fresh installations of 6.2.19 using the built-in database
(the default), and most likely fresh installations onto MySQL. Who was not:
every upgrade of an existing installation — upgrades run the upgrade scripts,
which were clean — and existing servers, whose databases already exist.
How it was caught

By the installer smoke test, which installs every release on a throwaway
machine — and which has itself been fixed to be worth more: the silent-install
step is now bounded at ten minutes instead of hanging with the job, writes and
keeps the installer's own log, and on a database failure re-runs the setup tool
and prints the stderr the real error had been going to all along. The 6.2.19
hang produced no evidence in ninety minutes; the instrumented re-run named the
failing dialog and its exit code in ten.
Also in this release (since 6.2.19)

    IMAP THREAD (RFC 5256), both algorithms — THREAD=ORDEREDSUBJECT THREAD=REFERENCES — with real References-chain threading: conversation trees
    for the clients that ask for them, bounded by the same per-command ceilings as
    SEARCH and SORT. An adversarial review of the new code found and fixed a stack
    overflow reachable through a deep reply chain, an uninterruptible header pass,
    and a malformed-Date sort inversion, before any of it shipped.
    The release-signing workflow could not name its own repository and failed on
    its first run; fixed, and 6.2.19's assets were signed by the re-run. This
    release's assets are signed the same way.

Validated by the full regression suite against this binary, and by the installer
smoke test against this exact installer before the release was promoted from
pre-release.