This reminds me it was only five months ago a client sent a bug report about our software's e-mail notifications having broken layout. Turns out they were still using Outlook 2010, which only implements HTML 2.1 or some ancient standard that wasn't even HTML 4.01. We also learned that styling only applies to <table> elements, not <div> elements. So we re-wrote all <div>s to <table>s, but layout was still subtly broken. Eventually we decided it wasn't worth the hassle to consider an increasingly niche e-mail client that couldn't even bother to implement an HTML specification from 1999.
It’s not just Outlook 2010 that uses MSO, which is a buggy and incomplete implementation of HTML 3.2; the current stable versions of Outlook (for Windows) and Windows Mail do. This might be changing in the new version supposed to be released this year, not certain. MSO has had approximately two changes in the last 25 years (one to support high-DPI displays, can’t remember the other I know of).
> Eventually we decided it wasn't worth the hassle to consider an increasingly niche e-mail client that couldn't even bother to implement an HTML specification from 1999.
Glad you came around. This is probably the correct decision.
