I have a recurring problem where I try to search my emails for an item I purchased (e.g. “Zapper” in all folders for a fly zapper purchased from an online marketplace). I gmail I find the results come up but in emClient they do not. I have to always resort to logging on to my gmail to do searches which is not really what I want to be doing (i.e. use two mail programs).
Example below of the rendered HTML email in emClient and in Gmail:
Also make sure you are searching “All Folders” in the dropdown field, and that you have checked "Subjects, Sender, Recipients, Notes, Body and Attachments in the search options.
Also sometimes “deselecting” Use server search can make a difference as well.
See the eM Client online documentation Search help below.
Lastly eM Client might also not be finding all your Gmail account messages yet “if they have all not been fully downloaded”. You can check that by clicking “All Mail” under your Gmail account and then click “Refresh”. Then click the dropdown on the right of Refresh and click “Show Operations”.