The only reason I had to drop proton mail as my main email address provider, was the lack of this function. I am just waiting for them to find a way to search by text, and I will go back to proton. Any idea when proton will be able to develop this?

http://www.reddit.com/r/ProtonMail/comments/2zks1m/what_features_would_you_like_added_to_protonmail/cs8ajx9

A fundamental feature!!

I have already suggested some time ago this functionality, because searching only the object is frequently not enough.

Search Email Text