Thursday, September 06, 2007

Adding an X-header in an Exchange Routing Transport Agent in Exchange 2007

This week I’ve been looking at Transport Agents which are the replacement to Transport Event Sinks in Exchange 2007. After the initial struggle of finding some decent information to get going these Agents are surprising easy to code and have a bunch of powerful functions that are more readily available then they were when compared to SMTP transport Event Sinks.

Getting Start info

If you’re looking for info on getting start the first place is this simple sample . One piece of advice is before you look at installing a Transport Agent making sure you know how to disable or remove one first.

There are two types of Transport Agents Routing and SMTP which one you use really depends where in the Transport Pipeline you want to intercept the message. I choose a Routing Transport agent because I wanted to be able to add an X-header to a message regardless of whether the message arrived via SMTP or if it was sent locally on a Mailbox server (if you are looking to do this in a SMTP Transport agent there is a X-header Sample in the Exchange 2007 SDK). The Transport Architecture document describes the process of Mail routing via the Hub server.

Once you get over modifying the subject you may want to start modifying the rest of the message this is where it starts getting hard and the information starts to get a little scarcer. Depending on what type of message you’re dealing with you may need to cope with MIME and TNEF formats. The later being a slightly harder thing to deal with for serialized messages most of the time MIME should be enough. So I would recommend reading the following MIME Architecture document from the SDK. Being able to deal with a serialized message in the MimeDocument Class is pretty cool and very powerful. You should always be carefully that any modifications you do make to a message aren’t going to mean that message breaks the Email RFC’s.

Getting down to the code

There are a number of different events you can hook into with a Transport Agent the one I was interested in was the OnSubmittedMessage. The event occurs just after the message is submitted because I only want to modify the headers content conversion shouldn’t really be an issue. The code is rather simple it first looks to see if there is a Xheader within the message already with the Name i want to use. If there isn't it creates a new Text header and inserts it before the last header in the current header list in the root MIME document.

I’ve put a download of the Transport Agent here the the main code itself is the following Event Handler

public class XHeaderRoutingAgent : RoutingAgent
{
public XHeaderRoutingAgent()
{ base.OnSubmittedMessage += new SubmittedMessageEventHandler(XHeaderRoutingAgent_OnSubmittedMessage);
} void XHeaderRoutingAgent_OnSubmittedMessage(SubmittedMessageEventSource esEvtsource, QueuedMessageEventArgs qmQueuedMessage)
{
MimeDocument mdMimeDoc = qmQueuedMessage.MailItem.Message.MimeDocument;
HeaderList hlHeaderlist = mdMimeDoc.RootPart.Headers;
Header mhProcHeader = hlHeaderlist.FindFirst("X-MyProcess");
if (mhProcHeader == null)
{
MimeNode lhLasterHeader = hlHeaderlist.LastChild;
TextHeader nhNewHeader = new TextHeader("X-MyProcess", "Logged00");
hlHeaderlist.InsertBefore(nhNewHeader, lhLasterHeader);
}

}

}

12 comments:

Kai said...

Hi Glen,

What I'm trying now to do is catch all email coming to the recipients on our exchange box, and then grab the subject line from them.

We will not be deploying an edge transport role due to insufficient hardware, so I'm having in mind to hook it to the OnSubmittedMessage event. Does incoming email from other servers go through OnSubmittedMessage too?

Your input will be much appreciated.

Glen said...

Depends what you mean by other servers are they all Exchange 2007. Exchange 2007 routes all mail that is submitted no matter what the source via a Hub server. So as long as you have the agent on each Hub Server where mail is routed you should see it should fire OnSubmittedMessage when the message is routed through that Hub Server.

If you have a number of servers you need to look at your routing architecture and understand how message routing differs in Exchange 2007. Eg Hub to mailbox server is over RPC etc.

Kai said...

OnSubmittedMessage just by its name suggests to me that it's an event fired when the exchange server is sending outbound mail (to whatever server, be it the same box or to gmail or hotmail or something).

I'm just basically wondering if I'm receiving email from hotmail or gmail on that exchange box, if OnSubmittedMessage will be fired for them.

Thanks for your prompt reply.

Glen said...

Well im far from an expert on this but

Submitted is referring to the message being submitted to the HubServer. Going out on a limb here this Event fires Pre Cat eg meaning if i send a message to a distribution list you will hit this event before the list is expanded by the categorizer. OnRoutedMessage fires Post cat when the server has worked out where it needs to send the message.

In the example your talking about yes it would fire. Basically your STMP receive Connector will get receive the message from hotmail.That mail would then be put in the submission queue which would then fire this event. After its been categorized and the server works out which mailbox server it needs to send this message it would then fire OnRoutedMessage Event.

This is my understanding at the moment some of which is based on assumptions (especially the CAT stuff). I suggest you test it yourself Agents are easy to write and you'll find out pretty quickly what does and doesn't work. You might also want to try posting a question on the Exchange Dev Forum http://forums.microsoft.com/TechNet/ShowForum.aspx?ForumID=838&SiteID=17 where you should get a more technically correct answer.

Cheers
Glen

Kai said...

Yeah I've been writing agents already to test several things. I'm unable to test for what I'm questioning because our exchange box is not actually wired to the internet yet and as such I can't test for the external servers.

Looking at this diagram http://technet.microsoft.com/en-us/library/Aa996349.6f548b64-6ac2-4e98-9098-69ad6cd9f569(en-us,TechNet.10).gif
however I'm increasingly convinced it is as you said.

Thanks lots for your help on this, and well done on the blog - I have, in the past month, found at least 2 articles which is directly helpful to what I'm doing at work.

=)

Oscar Trimboli said...

Wow – awesome, great insights – thought I would introduce you to my world

rishi shah said...

I just want to change an existing Header and i really cannot seem to get this working.

I want to change the Header return-path so tha the address shown to external parties is re-written to someething else.

I know my rule is working to an extend because when i use the transport rule on an edge server, rather than re0writting the existing header, it actually adds the header to the end of the entire header itsself which really has no effect.

So how can i do it? I do not wish to re-write the address for the whole domain, but just for one user only. Any ideas what i should use as the Header vaule i should be changing in the Transsport rule on the edge server to make this work?

Thanks.

rishi at rishishah dot co dot uk

John said...

I would like to add a header of VBR to each message i.e. a digital signature to say its from our mailserver


I am not exactly sure this is the best method but so far it look's like it for our exchange server
what is your opinion ?

how would you do it given the chance ?

your thoughts would be really appreciated !

regards

John Jones

p.s. I have to do this for exchange 2000, 2003 and 2007 I am aware that I might have 2 differant models...

Matheus said...

Hi Glen,

Thanks, thanks, thanks!
I'm searching exactly what u post here. Great job!

Matheus Cavalieri
matheusbh at. gmail dot com

Johan Dreyer said...

Hi Glenn,

I would like to rewrite the TO, and CC envelope address for all email sent to external contacts so that it replaces the internal Primary SMTP Address of the contact with their actual External SMTP Address.

Any help you can give would be greatly appreciated.

Glen said...

Have a look at http://gsexdev.blogspot.com/2009/01/from-address-rewriting-in-transport.html which should help.

Cheers
Glen

Steve Bird said...

Hello All.. We have an Exchange 2007 server , and we have a need to add a text header to all outgoing emails with the subject and the recipient in. does anyone have any suggestions or help please..