This article describes some of the headers which VPOP3 can add to messages. Note that some of these may be added by customisable scripts used by VPOP3, so may not match exactly, but the descriptions below are for the defaults distributed with VPOP3.
The custom headers added by VPOP3 will all begin with the X-VPOP3 text.
The X-VPOP3-RCPTTYPE header shows 'how' the message arrived at you. This can be useful for diagnosis and things such as autoresponder filters.
The ways the message are indicated by letters, and there may be more than one letter - eg if a message is sent to two people: you and someone of whom you are an assistant, the X-VPOP3-RCPTTYPE will show that you received the message because it was sent to you (D) and because you are an assistant (A)
The types reported are:
This header is only added when the message is finally delivered to your mailbox
This header contains the original recipients of the message. So, if you are the originally intended recipient, it will list your email address, or if you received the message as someone's assistant, it will contain the email address of the person of whom you are the assistant.
If there were several original recipients which led to you receiving the message, then there will be more than one X-VPOP3-ORIGRCPT header line.
This header is only added when the message is finally delivered to your mailbox