Sometimes emails are long and need to be read carefully. Currently, Proton Mail does not allow a received email to be read in full screen either through a popup or by toggling out the columns on the left (listing folders or individual mails). The 'toggle out' function is currently offered by Gmail and Outlook.

I find it frustrating that on a laptop I can only get about 30% of the screen width to read an incoming email. It increases the risk of missing or misconstruing important content.