In exchange server  create some TransportRule. Like this:

New-TransportRule "Approval1" -HeaderContainsMessageHeader "X-Approval" -HeaderContainsWords "test1-Approval" -ModerateMessageByUser test1@corp.com,test2@corp.com

New-TransportRule "Approval2" -HeaderContainsMessageHeader "X-Approval" -HeaderContainsWords "test2-Approval" -ModerateMessageByUser test3@corp.com,test4@corp.com

When user send email , and test2 user approval this email , I want write some data (from,to,subject,body,sendtime,approvalUser,approvalResult) to sql server ,

In custom RoutingAgent  class OnSubmittedMessage method,

if MapiMessageClass =IPM.Note.Microsoft.Approval.Reply.Approve  this mail is approval mail, and MapiMessageClass= IPM.Note.Microsoft.Approval.Request.Recall or IPM.Note.Microsoft.Approval.Request.reject .

but I dont The original message, The relationship between them was found.

Thanks all.

You would need to use the PidTagReportTag property https://msdn.microsoft.com/en-us/library/ee160822%28v=exchg.80%29.aspx to relate the message (although this would contain information about the Message that is being stored in the Arbitration mailbox). But this property would be both present in the Moderation request and Moderation response. To read that property in the Transport Agent you will need to use the TNEFReader eg http://gsexdev.blogspot.com.au/2011/04/reading-custom-mapi-properties-in.html

Cheers
Glen