Shadow redundancy is an Exchange-specific feature (beginning with Exchange 2010) that provides a measure of fault tolerance when relaying email messages with SMTP.
The sending Exchange server sends the EHLO
command.
EHLO smtp_sender.example.com
The receiving Exchange server may advertise that it supports shadow redundancy with the XSHADOW
keyword.
250-smtp_receiver.example.com
250 XSHADOW
The sending Exchange server can then use the XSHADOW
command, thus informing the receiving Exchange server that it plans to utilize this feature.
XSHADOW MGE5N2Q4YjgtNTg4MC00MGYzLWEzNWUtOWE3ZDk4ZGJjMDFlQFVDLUhDMS51bmlib3gubWVA
Question #1 - What is the value of the string that follows the XSHADOW
command?
If the receiving Exchange server agrees, it replies with a 250
status code.
250 tStREZcEVUiXW96O4lqrJA==
Question #2 - What is the value of the string that follows the 250
?
At a later time, the sending Exchange server will use the XQDISCARD
command to query the receiving Exchange server to determine if it was successful in relaying the message.
XQDISCARD 50
Question #3 - What is the value of the string that follows XQDISCARD
?
If the receiving Exchange server has successfully relayed the message, then it will reply with a 250
status code.
250 845e8916-2efb-444f-b7ea-5e676ddfa6a5
Question #4 - What is the value of the string that follows the 250
?
I've read that it's a unique ID for the message that was relayed, but I don't see where this ID was previously exchanged between the servers.