How to prepend all External email Subjects with [External Source]?

Prepending all external email subjects with [External Source] is a way to easily identify emails that come from outside the organization, and to help users be more cautious when opening or responding to those emails.

Steps to prepend all External emails subject with [External Source]

:- Go to https://admin.google.com/

:- Apps>Google Workspace> Gmail> compliance > Content compliance> Add another rule.

Give the NAME

Check mark Inbound

Add expressions that describe the content that you want to search for in each message

Add

Advanced content match

Location>Subject Match type >Not contains text

Here give the same message as

Then save Subject Prepend the custom subject Give the same message

Then save

Please find the below support article for your reference:-

https://support.google.com/a/answer/1346934?hl=en