PGP Partitioned is a format optionally used by Symantec in it's Encryption Desktop.
It's not an official standard, it does not have a content type. There is just some mailing thread describing it. (partitioned) PGP Partitioned is basically a word for "PGP/Inline Mail Body and each attachment encrypted / signed separately "
It can usually be identified by a "PGPexch.htm.pgp" Attachment containing the body of the mail as a HTML Page.
Symantec's Encryption Desktop can be configured to send PGP/MIME. This should be preferred.
Note: The GUI settings for do not seem to work, at least for some users, a solution is to edit the config filed of PGP Desktop according to: https://support.symantec.com/en_US/article.TECH164655.html
Why should PGP/MIME be preferred?
- PGP Partitioned is not standardized in an RFC.
- It does not properly handle encoding as it uses PGP/Inline.
- Attachments and the Text are encrypted / signed as different PGP Messages.
E.g. for a Signed and Encrypted Message with 10 Attachments a receiving MUA would have to show 10 different decryption and verification states. To do this securely and user friendly is nearly impossible.
An attacker could add or remove attachments to a mail or change the encoding specified in the mail header making this format inherently insecure.
The format was not designed with security or usability in mind but to work around Outlook and Exchange quirks. These quirks are no longer necessary as it is possible since Exchange 2010 and Outlook 2003 to send and receive proper PGP/MIME messages in Outlook.