Well, the point of a decentralized blockchain, is that EVERYONE has the data.

But only you have the key to unlock the encrypted data that is yours.

The entire blockchain should be encrypted, so that no one else can read your emails, but everyone has your emails, so that even if one copy of the data is gone, other people still have the data, so your emails are safe.

Keeping it encrypted means that only you can access your emails though.

I always recommend strong encryption, which is a technical term.