GpgOL: Error when moving opened S/MIME Mails with attachments on Exchange
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If an S/MIME Mail has attachments it cannot be moved while it is decrypted / visible.

I was able to reproduce this problem with an Exchange Server and latest Outlook

My understanding of this issue and the fix for it is that Outlook with exchange detects that our mails are S/MIME mails. As the attachments are modified by us outlook wants to save the changes on move. This fails because it can't do the crypto. Leading to the error. This also happens when such a mail is closed.

The trick is to save the mail after our changes were discarded so that the message class becomes a gpgol message class in MAPI. The problem with that is outlined in T4543