Thursday, September 20, 2007

Email and Attachment Archiving with a Transport Agent on Exchange 2007

I’ve been continuing on with building and learning about Transport Agents over the past couple of weeks and thought I’d share an agent I’ve found useful. The following agent is a simple archiving agent it saves the serialized version of the message from the Mimedocument class to an eml file in a directory assigning it a GUID as a filename to make sure its unique. It also enumerates though the attachments of a message and saves them to a separate directory using the attachment filename and the message guid to link the message and attachments. I also added some code into to delete pdf files that where smaller than 20 KB this was for testing purposes but it’s something I’ve used in the past in SMTP sinks to overcome certain issues.

Like the last Agent I posted this is a Routing agent I’m running on Hub Server the code is relatively simple to follow. To do the attachment processing I’ve used the new EmailMessage class that’s part of the Microsoft.Exchange.Data.Transport.Email namespace. The cool thing about this class is it does provide a level of abstraction above TNEF and MIME. So if say you’re sending a meeting appointment internally to another user and you have attached a document if you where to parse this at the MIME level the message and attachment would be in TNEF format (good old winmail.dat) but the EmailMessage class allows you to enumerate though any attachments in the calendar invitation without needing to worry about using the lower level TNEF parsers. The one complaint I have about this class is that downloading an attachment is a little bit of a pain. After initially having problems with streams that would get corrupted intermittently I found Jon Skeet’s page http://www.yoda.arachsys.com/csharp/readbinary.html which had a function that worked well.

The other challenge I had was with removing particular attachments, generally deleting objects while enumerating though a collection isn’t the best of programming practices. Sometimes enumerating the collection in reverse can overcome this issue but for some reason when I did this with the attachment collection it would always give me an issue when I removed an attachment. So the solution I came up with for this was just to store the attachments that I wanted to delete in an arraylist during the initial attachment check and then loop though the arraylist at the end and delete those objects which seemed to work okay.

The one thing this agent is yet to handle is processing attachments within embedded messages which I think will be a separate post.

I’ve put a download of the code from this post here the code itself looks like

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Diagnostics;
using Microsoft.Exchange.Data.Transport;
using Microsoft.Exchange.Data.Mime;
using Microsoft.Exchange.Data.Transport.Email;
using Microsoft.Exchange.Data.Transport.Smtp;
using Microsoft.Exchange.Data.Transport.Routing;
using Microsoft.Exchange.Data.Common;

namespace msgdevExchangeRoutingAgents
{
public class EmailArchivingFactory : RoutingAgentFactory
{
public override RoutingAgent CreateAgent(SmtpServer server)
{
RoutingAgent raXheader = new EmailArchivingRoutingAgent();
return raXheader;
}
}
}

public class EmailArchivingRoutingAgent : RoutingAgent
{
public EmailArchivingRoutingAgent()
{
base.OnSubmittedMessage += new SubmittedMessageEventHandler(EmailArchivingRoutingAgent_OnSubmittedMessage);
}

void EmailArchivingRoutingAgent_OnSubmittedMessage(SubmittedMessageEventSource source, QueuedMessageEventArgs e)
{
//Archive Message
String MessageGuid = Guid.NewGuid().ToString();
Stream fsFileStream = new FileStream(@"C:\temp\archive\messages\" + MessageGuid + ".eml", FileMode.OpenOrCreate);
e.MailItem.Message.MimeDocument.WriteTo(fsFileStream);
fsFileStream.Close();
//Archive Any Attachments Check for pdf attachments under 20 K and delete
ArrayList adAttachmenttoDelete = new ArrayList();
for (int index = e.MailItem.Message.Attachments.Count - 1; index >= 0; index--)
{
Attachment atAttach = e.MailItem.Message.Attachments[index];
if (atAttach.AttachmentType == AttachmentType.Regular & atAttach.FileName != null)
{
FileStream atFileStream = File.Create(Path.Combine(@"C:\temp\archive\attachments\", MessageGuid + "-" + atAttach.FileName));
Stream attachstream = atAttach.GetContentReadStream();
byte[] bytes = ReadFully(attachstream, (int)attachstream.Length);
atFileStream.Write(bytes, 0, bytes.Length);
atFileStream.Close();
atFileStream = null;
bytes = null;
// Find Any PDF attachments less then 20 KB
if (atAttach.FileName.Length >= 3)
{
String feFileExtension = atAttach.FileName.Substring((atAttach.FileName.Length - 4), 4);
if (feFileExtension.ToLower() == ".pdf" & attachstream.Length < attachstream =" null;" atattach =" null;" enumerator =" adAttachmenttoDelete.GetEnumerator();" initiallength =" 32768;" buffer =" new" read =" 0;" chunk =" stream.Read(buffer,"> 0)
{
read += chunk;

// If we've reached the end of our buffer, check to see if there's
// any more information
if (read == buffer.Length)
{
int nextByte = stream.ReadByte();

// End of stream? If so, we're done
if (nextByte == -1)
{
return buffer;
}

// Nope. Resize the buffer, put in the byte we've just
// read, and continue
byte[] newBuffer = new byte[buffer.Length * 2];
Array.Copy(buffer, newBuffer, buffer.Length);
newBuffer[read] = (byte)nextByte;
buffer = newBuffer;
read++;
}
}
// Buffer is now too big. Shrink it.
byte[] ret = new byte[read];
Array.Copy(buffer, ret, read);
return ret;
}
}




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);
}

}

}