However, mailbox can still be encrypted with pgp, and has some built in supports which make this easier.
One problem I had with proton/tuta is that you cannot use a third party app due to the encryption, which you can with mailbox. A problem I have with mailbox is that it does not support fido2 for login or 2fa, which could be a security concern.
This is one of the first where I struggled to read it correctly. I think the colours are making the effect worse here.