Though I work to manage it well, I spend a good bit of time in email. Specifically, I use Gmail, both personally and for work.
One nit-picky interface detail that has always bugged me is Gmail’s handling of highlighted text. It’s useful on face value, but if you copy and paste text from any email that has highlighted search terms, the highlighting will be included when you paste that text into a new message or draft.
You can get around this by using Paste and Match Style in the Edit menu (or Shift+Option+Command+v), but that technique will strip any other formatting out as well (text ornamentation, bullets, etc.).
I wish there were a way to turn highlighting off by default, but the only way to toggle that option currently is by choosing an option from the “More” button after each individual search. Here’s where you find it: