After verifying a message or decrypting it, gpgol wants to update the message, for example to save a green category,
as visible on the given screenshot
This category and other changes on the message performed by gpgol will trigger an update of the original message. Exchange can deal with this update easily, but we are developing an alternate mapi-http implementation using an IMAP server as its backing store. Emulation the mutability of exchange messages over an imap server is complicated tasks and we would like to know if a "read only" registry option in gpgol already exist or was feasible.
I can easily understand that improving gpg4win compatibility with bluemind and its mapi endpoint is not a priority. If you could point us in the right direction in your addon code we could provide a PR for a read-only option when opening messages.