exchange-server - Building 3rd party content filtering plugins for Exchange server

Question

We want to build a 3rd party plug-in to assess inbound and outbound messages according to certain criteria. Then we want to either change the message metadata or forward it, if it meets a particular criteria. It cannot be done with regexes or keywords. It is really a custom set of actions.

I found several leads, but it is not clear whether it can be achieved. Here are the leads:

• https://docs.microsoft.com/en-us/previous-versions/office/office-365-api/api/version-2.0/mail-rest-operations#GetMessages - Outlook API is being deprecated but it seems that Graph API is taking over the functionality.
• Exchange Web Services (EWS): https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-access-email-as-a-delegate-by-using-ews-in-exchange - but it's unclear whether our service can access user's messages with administrative privileges.
• Exchange Online Protection: https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/exchange-online-protection-overview?view=o365-worldwide - but is there a plug-in architecture?
• Built-in content filtering: https://docs.microsoft.com/en-us/exchange/antispam-and-antimalware/antispam-protection/content-filtering?view=exchserver-2019 - again, is there a way to embed a plug-in?
• Finally, transport agents: https://docs.microsoft.com/en-us/exchange/mail-flow/transport-agents/transport-agents?view=exchserver-2019 - that seems to be just the ticket, but I wonder if there's a catch?

Dear Exchange gurus, what the advantages and the disadvantages of every approach?

标签： exchange-serverexchangewebservices