Are you intent on finding a provider or are you open to the idea of setting up your own email system? I recently setup my own email server using TLS for SMTP and IMAP/S for retrieval. It’s all hosted on a machine with a single processor, 2 GB of RAM, 20 GB of disk and it uses Linux. It takes a while to setup, but the end result is your own private server to which no one has access except you and those you designate.
Just throwing it out there. Otherwise, I wish you luck in your discovery. I’m not familiar with any providers who I would trust.
I do not possess the knowledge or experience to accomplish this. I do thank you for your comments.