The reason why it is still a major version is that the developing company linked development of the free Home version with the commercial version the latter received lots of new features. MailStore Home 12.0 is a major new version but the feature additions aren't that spectacular.
Another option provided by the installer is to install MailStore Home as a portable version which makes it an ideal tool to carry an archive of emails with you on a USB Flash Drive or other storage device. You can install the new version on top of existing versions to upgrade them automatically. Installed versions of the program may notify you of the new version if you have enabled automatic update checks.
MailStore Home 12.0 is available as a download on the developer website. Tip: read how you can speed up Thunderbird (and other local clients) by archiving emails. The program is updated regularly with new features and support for new versions of Windows or new software email programs. Back then, we found it to be an excellent program for backing up online email accounts and local accounts in programs such as Microsoft Outlook or Mozilla Thunderbird. We have followed development of the email software since 2011 when we released our initial review of MailStore Home.