Append -External- in Subject and/or body of e-mail BUT don't if S/MIME Signed/Encrypted

%3CLINGO-SUB%20id%3D%22lingo-sub-768523%22%20slang%3D%22en-US%22%3EAppend%20-External-%20in%20Subject%20and%2For%20body%20of%20e-mail%20BUT%20don't%20if%20S%2FMIME%20Signed%2FEncrypted%3C%2FLINGO-SUB%3E%3CLINGO-BODY%20id%3D%22lingo-body-768523%22%20slang%3D%22en-US%22%3E%3CP%3EI'm%20guessing%20this%3A%3C%2FP%3E%3CP%3E%3CA%20href%3D%22https%3A%2F%2Fwww.securit360.com%2Fblog%2Fconfigure-warning-messages-office-365-emails-external-senders%2F%22%20target%3D%22_blank%22%20rel%3D%22noopener%20nofollow%20noopener%20noreferrer%20noopener%20noreferrer%22%3Ehttps%3A%2F%2Fwww.securit360.com%2Fblog%2Fconfigure-warning-messages-office-365-emails-external-senders%2F%3C%2FA%3E%3C%2FP%3E%3CP%3E%26nbsp%3B%3C%2FP%3E%3CP%3EBut%20instead%20of%20fallback%20action%20Wrap%2C%20use%20instead%20fallback%20action%20Ignore.%3C%2FP%3E%3CP%3E%26nbsp%3B%3C%2FP%3E%3CP%3EI'm%20thinking%20that%20the%20processing%20should%20fail%20on%20both%20an%20S%2FMIME%20Signed%20or%20an%20S%2FMIME%20Encrypted%20message%2C%20and%20then%20it%20should%20just%20ignore%20the%20rule%20as%20per%20the%20fallback%20option.%3C%2FP%3E%3CP%3E%26nbsp%3B%3C%2FP%3E%3CP%3EWe%20use%20S%2FMIME%20signed%20and%20encrypted%20messages%20all%20the%20time%2C%20I%20want%20to%20make%20this%20external%20marking%20thing%20happen%20for%20phishing%20protection%2C%20but%20I%20absolutely%20do%20not%20want%20to%20break%20our%20S%2FMIME%20or%20the%20workflow%20at%20all.%3C%2FP%3E%3CP%3E%26nbsp%3B%3C%2FP%3E%3CP%3EPlease%20someone%20confirm%20from%20Microsoft%2C%20or%20other%20users%20that%20have%20done%20this%20in%20their%20365.%3C%2FP%3E%3C%2FLINGO-BODY%3E%3CLINGO-LABS%20id%3D%22lingo-labs-768523%22%20slang%3D%22en-US%22%3E%3CLINGO-LABEL%3EExchange%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3EOffice%20365%3C%2FLINGO-LABEL%3E%3CLINGO-LABEL%3ESecurity%3C%2FLINGO-LABEL%3E%3C%2FLINGO-LABS%3E
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Occasional Contributor

I'm guessing this:

https://www.securit360.com/blog/configure-warning-messages-office-365-emails-external-senders/

 

But instead of fallback action Wrap, use instead fallback action Ignore.

 

I'm thinking that the processing should fail on both an S/MIME Signed or an S/MIME Encrypted message, and then it should just ignore the rule as per the fallback option.

 

We use S/MIME signed and encrypted messages all the time, I want to make this external marking thing happen for phishing protection, but I absolutely do not want to break our S/MIME or the workflow at all.

 

Please someone confirm from Microsoft, or other users that have done this in their 365.

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