To:

To:

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The primary recipients

RFC2822

The To: header lists one or more of the recipients of the mail message. Other headers, such as Cc: , also list recipients.

If the header of a mail message lacks recipient information ( To: , Cc: , and Bcc: header lines), pre-V8.7 sendmail added an Apparently-To: header line and put the recipient's address from the envelope into the field of that header. Beginning with V8.7, the way a message with no recipients is handled is determined with the NoRecipientAction option (NoRecipientAction).