I think there’s some confusion happening here.
Outlook accepts some links with the format outlook://inbox and that works in Logseq no problem. This style of link with the double slash is used when referencing locations in outlook, such as the inbox. But that does not work when directly linking to an email. In this case the link needs to be of the format outlook:emailidstring. No double slash. Outlook will return an error if there is a double slash when referencing an email id.
If I paste a URL with the format outlook:emailidstring into a browser address bar, or into the Windows run dialog box it works fine. The OS is handling the URL correctly. However in Logseq, it creates a page with that name and treats it as an internal link. This is definitely something on the Logseq side, it is not passing that URL to the OS for handling.
I’ve found a workaround however. It works if you embed the link as HTML. So try creating the link using the following format.
@@html: <a href="outlook:messageidhere">click me</a>@@
On my system the above works.