Skip to main content

Processing BCC's in Exchange Transport Agents

One of the most important learning points when thinking about programing or designing Transport agents is to understand the different between a P1 (Delivery Envelope) and P2 (Display Envelope)

The P1 (Delivery Envelope) contains the recipient To and From information that is transmitted to the MTA server be it Exchange or any other SMTP server in the SMTP conversation and is the actual information that will be used for delivery of the message. Eg the Evaluating MTA will only examine the P1 recipients to determine what recipients a message would be delivered to.

The P2(Display Envelope) contains all the information that that the user will see when they receive the message this includes the From, To ,CC and Subject of a message. The important point to understand is that the MTA that is processing the message doesn’t look at these headers to determine whom to deliver the message to.


One of the things that confuses a lot of people when they look at messages via an API or within an Transport Agent is that most API’s include the ability to set and get BCC address’s but they will always appear blank when you attempt to read them for example when a message is passing through the transport pipeline. The simple explanation for this is if you have understood about P1 and P2 recipients is that BCC’s when a message is submitted become P1 recipients of the message for the first MTA to process but they are never added to the P2 envelope. From the MTA’s perspective because delivery of TO, CC or BCC are treated exactly the same these elements are merely display information and the MTA just treats these recipients as another RCPT TO entry. To detect BCC in a Transport Agent you can do two things the first is reconcile the P1 Recipients against the P2 Recipients if you find a P1 recipient that doesn’t have a matching P2 entry then you can assume that this is either a BCC or potentially an alternate or journal recipient. The other way is to look at the Microsoft.Exchange.Transport.RecipientP2Type EnvelopeRecipient.Properties Property this returns an Integer that tells you what type of recipient each P1 envelope entry is.

For example

foreach (EnvelopeRecipient envelopeRecp in QueuedMessage.MailItem.Recipients) {
object RecpType = null;
if (envelopeRecp.Properties.TryGetValue("Microsoft.Exchange.Transport.RecipientP2Type",out RecpType))
case 1 : // Process To
case 2 : // Process CC
case 3 : // Process BCC

Popular posts from this blog

Export calendar Items to a CSV file using EWS and Powershell

Somebody asked about this last week and while I have a lot of EWS scripts that do access the Calendar I didn't have a simple example that just exported a list of the Calendar events with relevant information to a CSV file so here it is.

I've talked on this one before in this howto  but when you query the calendar folder using EWS you need to use a CalendarView which will expand any recurring appointments in a calendar. There are some limits when you use a calendarview in that you can only return a maximum of 2 years of appointments at a time and paging will limit the max number of items to 1000 per call. So if you have a calendar with a very large number of appointments you need to break your query into small date time blocks. In this example script I'm just grabbing the next 7 days of appointments if you want to query a longer period you need to adjust the following lines (keeping in mind what I just mentioned)

#Define Date to Query
$StartDate = (Get-Date)
$EndDate = (Ge…

EWS Managed API and Powershell How-To series Part 1

I thought I'd start the year with a series of posts that goes back over the basics of using the EWS Managed API from Powershell and provides a modular remarked example that you can easily cut and paste to build your own scripts. Along the way in this series I'll show a whole bunch of examples around specific things.

As a starting point for versions this will be Powershell Version 2.0  and the EWS Managed API 1.1 (which will soon change to 1.2 once released)

The starting point for any EWS script your going to write is connecting to Exchange for which there are three important pieces of information you will need. Firstly you need to know the version of Exchange your running in this script its going to be held in the following variable

$ExchangeVersion = [Microsoft.Exchange.WebServices.Data.ExchangeVersion]::Exchange2010_SP1

Other valid values for Exchange 2007 would be

$ExchangeVersion = [Microsoft.Exchange.WebServices.…

Writing a simple scripted process to download attachmentts in Exchange 2007/ 2010 using the EWS Managed API

Every complicated thing in life is made up of smaller simpler building blocks, when it comes to writing a script (or any code really) the more of these little building blocks you have to figure out the more the process of solving a problem can become bewildering. The Internet generally provides you with lots of half eaten sandwiches of information something someone else has taken a bite out but a lot of the time half done, and as with any code its usefulness declines over time as new and better API's and methods are derived. In this post I'm going to go through a simple scripted process that hopefully covers a few more of these smaller building blocks that you might face when asked to come up with a simple costless solution to perform an automated business function with a script.

So the process im going to look at is one that comes up a lot and that is you have an Email that comes into to certain mailbox every day with a certain subject in my case "Daily Export" this …
All sample scripts and source code is provided by for illustrative purposes only. All examples are untested in different environments and therefore, I cannot guarantee or imply reliability, serviceability, or function of these programs.

All code contained herein is provided to you "AS IS" without any warranties of any kind. The implied warranties of non-infringement, merchantability and fitness for a particular purpose are expressly disclaimed.