How to save Outlook mails as .msg file with categories and other details?

It is easy to save emails in Outlook VBA with MailItem.SaveAs

But I don't see any option to save additional details like i.e. the Author and Categories.

The 3rd party program MessageSave allows to save mails with Categories and Author in .msg format. In Windows Explorer the columns Author and Categories show the same information like in Outlook.

Does anybody know how to save messages using Outlook VBA including these additional information?

I bought MessageSave and it's a good program but they don't allow their save function to be used in VBA. The only workaround is to let MessageSave save messages when they "arrive" in a specific folder. If necessary I can use this function but this is just a workaround.

Here is a sample how the emails saved with MessageSave are shown in Windows Explorer: