I might be helpful if the main webpage https://mailinabox.email/ under Status Current Version stated the correct version, and the release notes linked under the current version section also had the correct information about V0.53a.
They both say V0.53 and say nothing about V0.53a.
I understand the situation as described by Shayne, but it is confusing to users when the software tells you “A new version of Mail-in-a-Box is available. You are running version v0.53. The latest version is v0.53a. For upgrade instructions, see https://mailinabox.email.” but you can not find anything about this new version where it normally is located.
Even if people do not need to update if they already have V0.53 - then this should be in the release information linked on the main page.
I also could not find any information, and had to search for “V0.53a” to find anything, and just found this thread.