How should an email message, represented as a single file, be added to a Maildir?

The naming conventions of Maildirs seem pretty elaborate. I downloaded a message from Outlook's web interface and added it to a Maildir by naming it added and putting it in a new folder. mbsync and mu4e seemed happy enough with the result, but I wouldn't be surprised if I ran into trouble by making a habit out of this. Is there a program to add a file to a Maildir in the right way? Ideally such an operation wouldn't require configuring and running a full-blown mail server on my machine.