TOPIC When a mail server collects mail using POP (Post Office Protocol), it relies on the recipient's name being in the mail header. If the mail server cannot find a local recipient in the email header, it will send the mail to the Postmaster. Email sent through mailing lists and or as a blind carbon copy (BCC) are two common situations where the intended recipient is not listed in the email header. DISCUSSION
The list of addresses included in the header fields (To: and CC:) are not used by an SMTP (Simple Mail Transfer Protocol) server to route mail to the final destination. The purpose of these fields is purely for display, and to allow email clients to reply, and perform other functions that have nothing to do with mail routing. Mail routing is achieved through a set of SMTP commands that a client sends to a server (or that one server sends to another server). These commands are separate from the message headers and body. Blind carbon copy, for example, is implemented by using the SMTP commands to route mail to the destination addresses, but not printing the BCC address anywhere in the message text itself. That way, the user receives the mail, but there is no evidence in any of the emails that this happened. The only evidence that the user received the mail would be located in the SMTP logs on a mail server. Similarly, mailing lists have the list address--not the individual user's address--printed as the destination in the header. Once mail is delivered to a POP mailbox, the information contained in an SMTP stream is lost. If the header text of the email does not contain the recipient information, the mail server has no way to regain that lost information to determine the true recipient of the message. When this happens, the mail server routes the mail to the local "Postmaster" account. Some mailing lists work correctly even if the mail appears to be addressed to the list, and not the user. These lists add additional fields in the header indicating the true destination of the email. In addition to addresses listed in "To:" and "CC:", the mail server looks for the following headers to find the destination: To see if you are experiencing this issue, you can inspect your full email header (most email clients have a "View Header" feature). Look for a local user account listed in the "To:" and "CC:" fields or any of the fields mentioned above. If you see no email address for your server listed, or if you see a local address in a field other than those mentioned above, then the mail server is behaving correctly in delivering this mail to the Postmaster. This limitation of the POP collection method can lead to the symptom described in article 86029: " AppleShare IP 6.x: Some Mail is Misrouted to Postmaster "
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| Document Information | |
| Product Area: | Apple Software; Communications-Networking |
| Category: | AppleShare |
| Sub Category: | AppleShare for Mac OS |
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