@far4 said in How does Vivaldi webmail compare to other popular email providers?:
Just read up on the features of pgp, it can do this.
It's been two decades since I last used PGP, but I did a quick search how it does this.
When I receive this message on my gmail, I can decrypt it with any of the three private keys. Any and one key.
That's because when you send a message to several receivers, it encrypts the message itself with a symmetric key (the same for all) then encrypts this key in the header of the document with the pubkey of the recipient.
https://www.quora.com/How-does-PGP-manage-to-encrypt-a-message-for-two-different-people
https://superuser.com/questions/554513/pgp-encrypt-single-message-for-multiple-recipients
https://security.stackexchange.com/questions/8245/gpg-file-size-with-multiple-recipients
If the message itself was encrypted with all pubkeys of all the recipients, it could not be opened by anyone. Only each header for each recipient is encrypted with the pubkey.