When sending/reading an email show if the email was sent/received securely
Gmail has this feature where we can see if it's secure or not.
Lifetime User commented
It seems there is now a small lock icon in the top right of a message (browser) or right side of the message listing (android, at least in 1.6.5+). Mouse-over on a purple lock says "end to end encrypted internal message" and dark grey lock says "external message, stored encrypted". It's a good start, but I know everything is stored encrypted - it is my protonmail inbox after all.
It would be great if that grey lock instead meant "sent over an encrypted channel TO protonmail" so I can identify if a site has just emailed me my password (!) and it wasn't sent over encrypted SMTP. Currently, I have to go digging in the headers...
free of google commented
Yes, a clear indicator of "yes, this email has only traversed secure channels (on the connections listed in the headers) between email server X and protonmail" would be nice.
To other commenters: there is no universal way of ensuring you get a read receipt (as many mail clients won't send them, or people are given the option and choose not to) and there is no way to delete email once it leaves protonmail. It's the way email works, sorry. If you have seen it at other services it was likely only functional with others on the same service as you.
I would like to be able to know whether or not an email has been delivered. Read and Displayed are not quite as important, to me, and Reb has a point, too, over inbound Read notifications potentially allowing someone to know if the recipient is online or not; so I would vote for being able to tell if an outbound email has been delivered (plus making it deletable if that can be done without compromising security), but would want to make anything inbound optional in order to keep my activities on the Protonmail side private and secure.
Matthew Wolffsohn commented
Heads-up to the commentators: This is not a 'read receipt' feature. This is a 'Has this email been subjected to STARTTLS or other such encryption features' feature.
If read receipts are added, they should be optional only, as I don't want anyone knowing whether I've read an email yet, or not. The moment the receipt is delivered, it is obvious to the sender that you are currently online. I'd rather that would be private.
The Newton email client has the "read notification" feature and it works well, but it's $49 a year! https://newtonhq.com/
Being able to verify "delivered", "displayed", or both is essential when dealing with important messages. I don't know the complicated code required to accomplish this, but other insecure email accounts do provide this feature. It would be very much appreciated to see it on the "upcoming" features being considered.
I remember decades ago in AOL where the sender had the ability to delete a sent email to another AOL user if it hadn't been opened by the receiver yet. Also, the sender got feedback when the receiver opened the mail.
The option to do that between ProtonMail users (in "settings" or attached to the entry in the contact list) would be good.
It is a MUST as it can determine the delete time /save time of emails.
Read receipt would be a great feature to add.