I'm using 5.4-B2012052801 on my LIVE server.
(I download it from viewtopic.php?f=10&t=21420
It runs no problem.
Today, I found B1944 on a download page.
hMailServer 5.4 - 1944 (692 downloads since 2012-08-08)
What is "1944", and which is the latest?
Go by release/build date..
* 1944 is newer and is OFFICIAL BETA RELEASE (as in from martin, creator of hmailserver).
* 5.4-B2012052801 is older than 1944 and an EXPERIMENTAL UNOFFICIAL TEST RELEASE (as in from me, a contributing developer of hmailserver).
Understand though that official releases do not have all changes that are in the experimental builds.. The experimental builds are just that.. A test bed for new features that might or might not make it into the official releases. You'd need to check the change-logs to know. Often experimental releases are used for "hot fixes" for issues people run into & need something ASAP & can't wait for official release. Usually those fixes make it into official releases but again you'd need to check the 2 change logs & compare.
Hope that helps clears it up.
Ps. Glad to hear you are using an experimental build & it's working well for you. I would not be hung up on using the 'latest' be it official release or experimental. Look at the changes & see if they matter to you & use your judgement.