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Showing posts from June, 2011

Processing BCC's in Exchange Transport Agents

One of the most important learning points when thinking about programing or designing Transport agents is to understand the different between a P1 (Delivery Envelope) and P2 (Display Envelope) The P1 (Delivery Envelope) contains the recipient To and From information that is transmitted to the MTA server be it Exchange or any other SMTP server in the SMTP conversation and is the actual information that will be used for delivery of the message. Eg the Evaluating MTA will only examine the P1 recipients to determine what recipients a message would be delivered to. The P2(Display Envelope) contains all the information that that the user will see when they receive the message this includes the From, To ,CC and Subject of a message. The important point to understand is that the MTA that is processing the message doesn’t look at these headers to determine whom to deliver the message to. BCC’s One of the things that confuses a lot of people when they look at messages via an API or within a
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