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Why didn't all recipients in the header receive the message?

If there were multiple recipients specified in the headers of a message and not all recipients received the message, check the following:

If you are not seeing one or more of the recipients listed in the delivery logs, it indicates one of two things:

  1. The sending server might send each copy of the message separately to each recipient. Check to see if there is another copy of the message in the Quarantine+ viewer.
  2. The sending mail server failed to send to those recipients.

The way the SMTP protocol works, it's the responsibility of the sending server to tell the receiving server who the recipients of the message are. The receiving server does not actually scan the headers to determine who the recipients of the message are. For anyone questioning whether this is really true, just think about recipients that are Bcc'd. They are never listed in the headers. This underscores the fact that the sending server specifies who is to receive the message during the SMTP conversation.

In summary, if the delivery logs we provide do not show one of the recipients, it indicates that the sending server did not actually send the message to that recipient. Contact the sender and have them work with their email administrator to resolve the issue.

Last updated June 7, 2022