I waited quite awhile before upgrading this retina to yosemite, "waiting for the bugs to get worked out". Now that I'm here, I find that most of the emails I receive (most of them are from Outlook users here on their PCs) are NOT line-wrapping the text.

A bit of googling found many users reporting this issue, and much confusion because some have the problem and some do not. The issue apparently only affects emails sent with an HTML-readable alternative. Something about the html tags not specifying a line wrap or specifying it auto or way too big, and Mac Mail just merrily provides you with a "convenient" horizontal scroll bar at the bottom. Entire large paragraphs can appear on ONE LINE that you have to scroll and scroll and scroll to read.

I looked around in Mail and failed to find a "wrap text" option, as is available in well, practically every word processor on the planet that has the possibility of not wrapping text. (pico/nano being the only exceptions?)

Several threads suggest this has been a problem in Mac Mail under Yosemite for the last several versions, and that Apple may have no intention of ever fixing it in 10.10. ("wait for El Capitan!")

Is there a fix in Yosemite? (many users are resorting to hitting Reply to read their emails, because text wraps properly in the editor)

Have you tried Airmail 2 from the App Store?

I'm probably too proud to pay $10 for a bug fix

I recall a similar problem in Mail occurring two or three times in the past. Each time the fix required an update from Apple to resolve, but I have no idea what the problem specifically involved or the code changes it took to resolve it. 😟