The most common problem I personally have faced when setting up my notes in Evernote for postach.io, was getting the font to appear the same on the blog. Quite often the font would look right in Evernote, but then appear different on the blog - for example different paragraphs would appear differently.

The quickest way, and so far the only way to fix this, is to use Format/Simplify Formatting in Evernote.