Limit number of recipients in an email - Google Apps

Question

We are trying to Limit number of recipients in To, CC and Bcc fields using following regular expression, however not functioning as required. Please help.

Full headers / Recipient headers matches regex - ([^@]*@){3,}

Answer 1

Without much to go on in your original post you I offer this rather bleak answer which will match 1, 2 or 3 email addresses that adhere to RFC 5322:

(?:(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])[,;\s]*){1,3}

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Answer 2

This is what I use against "Recipients header" in a Compliance policy in Google.

^[^@](\@[^|]){6,}$