[ACCEPTED]-What is the effect of a Precendence: bulk header on e-mail messages-gmail
The exact meaning of
Precedence: isn't standardised, but 11 it prevents some mail servers from sending 10 vacation and bounce messages, and may be 9 used by service providers to deprioritise 8 bulk mail during busy times so that "personal" mail 7 continues to be delivered quickly.
Non-standard, controversial, discouraged. Sometimes 6 used as a priority value which can influence 5 transmission speed and delivery. Common 4 values are "bulk" and "first-class". Other 3 uses is to control automatic replies and 2 to control return-of-content facilities, and 1 to stop mailing list loops.
See the answers to this question, as well as RFC 3834.
In short, the 5
Precedence: header is non-standard. Google's recommendation 4 is perhaps just a way to give a hint to 3 their spam filters that you really did intend 2 to send out 500k+ emails from your server 1 (as opposed to one abused by spammers).
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