There’s a particular behaviour in Outlook for Mac, that for several years I have thought was a bug. If you reply to an email, you often only get some of the text from the original email, rather than the entire email being copied into the reply. Like this:

This week (after having a Mac for almost 4 years) I stumbled across the reason. It turns out that if you select text in the original email, only that text is quoted.

The feature has been there since at least Outlook for Mac 2011 and is there still in the latest Outlook for Mac. Certainly different behaviour to Outlook on Windows.

Unfortunately there is no way to disable the feature, so something to look out for in the future, now that I know what the cause is.