Send email to multiple recipients using Web API without them seeing entire recipient list

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  • Updated 4 years ago
How do you send an email to multiple recipients without each recipient seeing the other recipients using the Web API?

I've tried:
- Setting each recipient using the "to[]" parameter shows each recipient the entire recipient list.

- Setting each recipient using the "bcc[]" parameter works but then we also have to set something as the "to" parameter which then also gets the email. Plus this seems kinda hoky and I'm not sure if sending all emails as "BCC" affects deliverability/spam or reputation.

- Setting the recipients in the "to" value for the "X-STMPAPI" field. I'm not sure if this sends to each recipient individually but I did a test of a few hundred all sent to my gmail account as different addresses (using the plus sign) and noticed that only 1 email seemed to come through whereas using the normal "to[]" field I would see all 500 or so emails addresses listed that I sent to (when clicking on triangle button next to the "to: me" display). So I would see:,, ...

Am I missing something?
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Shaun Powell

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Posted 4 years ago

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Tim Jenkins, CTO

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Official Response

In order to accomplish what you want, the x-smtpapi field is your best, and probably only, option.

The reason gmail only delivered 1 copy, despite sending it to multiple addresses with the + option, is because of how gmail handles multiple copies of messages with the same smtp message-id field. At some point we'll make it so that the message-id is changed on every email with the x-smtpapi header, but for now whats happening is gmail thinks it is a duplicate message and just displays it once.