[7steps2much]

At least for the verifying that an email is original I agree with the other poster, DKIM exists for that purpose, to sign emails while in transit.

As for changed messages while synching, do your messages change after delivery? If not, a simple delivered after X would be sufficient.

[encryptluks2]

Yes messages can change after syncing. Using mbsync for example, if you change the contents of an email locally, there are no ways to detect the change. I guess the preferred solution may be to do a more generic sync directly from the mail server and bypass IMAP entirely.. not possible with most email providers like Gmail, Microsoft, etc. Hopeful to setup my own email server someday.