I use Trustifi to track emails I have sent. I see a map of where it was opened. Tracking is THE MOST IMPORTANT thing.

I enjoy seeing the IP address of the recipients location.

I liked seeing when the links or attachments were opened or downloaded.

I can see the time they opened the email. I know if they didn't open it. This has been very helpful. It prevented me from taking someone to court. they would have been blind-sided.

I can see if the recipient forwarded it to someone else.

I can make the email attachments open only once or give it so many days before they can't open it. If you add this, please don't let the recipient know that there is a change. That was a problem I had with Trustifi, they let the recipient know, and the person would take revenge on the action. I was able to change the status of what I wanted to do with the attachments after I sent the email.

I can send the email encrypted and secured.

I can put a password / text / phone number secured authentication on the email.

I can recall an email.

I can update an email already sent.

My problem with them is when I send it secured, it goes to SPAM and people don't get the secured emails. Trustifi use another email service to send it, like yours, but all the info I shared above, will be on their website. I like you, I just wish I could do everything I need there, in Protonmail.