sendgrid bcc not working

"SendGrid BCC not working" is rarely a silent delivery problem. In the v3 Mail Send API it almost always surfaces as an HTTP 400 Bad Request validation error before the message is ever queued. The bcc array lives inside each object of the personalizations array, and SendGrid validates it strictly.

What causes "SendGrid BCC not working"?

There are three distinct, documented triggers, all returned as validation errors from POST /v3/mail/send:

1. An invalid or empty bcc entry. Per SendGrid, "the bcc array, when used, must at least have an email parameter with a valid email address." An object with only a name, a malformed address, or an empty array element is rejected.
2. A duplicate address across to, cc, and bcc in the same personalization. This is the most common cause. SendGrid does not allow the same address in more than one recipient array within a single personalization object. The error reads: "Each email address in the personalization block should be unique between to, cc, and bcc. We found the first duplicate instance of [email address] in the personalizations.0.cc field." This is why a BCC recipient who is also in to or cc makes the whole call fail — and "BCC appears to do nothing" because the 400 means no email sent.
3. An invalid object shape — e.g. bcc set to a bare string instead of an array of email objects.

A subtler, non-error case: BCC is delivered, but the BCC recipient never appears in the visible headers (that is the point of blind carbon copy). If you only checked headers, BCC may actually be working.

How do I fix "SendGrid BCC not working"?

1. Give every bcc object a valid email (name is optional):

{
  "personalizations": [
    {
      "to":  [{ "email": "recipient@example.com" }],
      "cc":  [{ "email": "manager@example.com", "name": "Manager" }],
      "bcc": [{ "email": "archive@example.com" }]
    }
  ]
}

2. Deduplicate across to, cc, and bcc. Before building the request, collect every address in the personalization and ensure none repeats across the three arrays. If archive@example.com is in both to and bcc, drop it from one. Do this per personalization object — addresses can repeat across different personalization objects.

3. Respect the recipient cap. SendGrid counts every address in to + cc + bcc (across all personalization objects) toward a 1,000-recipient maximum per request, and no more than 1,000 personalizations per request. Large BCC lists that silently fail are often over this limit — split into multiple API calls.

4. Read the response body. A 400 returns an errors array, where each entry has a message and a field (e.g. personalizations.0.bcc.0.email) pinpointing the offending entry. Log it rather than assuming "BCC is broken."