What about Mail.app?

There may be the natural inclination to compare an application like Apple’s Mail.app to Outlook. The problem is that this is like comparing apples to oranges. Mail doesn’t have quality searching. Mail is for mail only, and doesn’t integrate calendar and contacts — those are separate apps. Mail has issues with confusing threads, application instabilities, crashes, and more.

Apple Mail also doesn’t have a whole series of features inherent to the Exchange protocol that Outlook does including online archives, delegation, syncing categories, client support for updating rules, and free/busy support. Mail also doesn’t support things like “streaming notifications” where the server tells the client that there’s new mail and you can even see new mail while you are syncing. In Mail.app, you have to wait for the next check of the folder. Not supporting these impacts performance — Apple Mail is a lighter weight application in many ways. That said, many if not most Apple Mail users report “crazy” (e.g., very high) levels resource usage.

Mail doesn’t consistently download mail either — often skipping a full download of a message until it gets to it later. Unfortunately, you don’t get to control when “later” is. Worse yet, Apple Mail is not kind to mail servers (see below). That’s why when you see a mail server straining, Mail just gives you an error that it couldn’t sync or move messages.

When it comes to benchmarking, sure, you could test things like launch speed and more. However, it’s more difficult to compare applications that operate differently, especially when Apple Mail is such an inconsistent performer, and often isn’t providing the same services.