Skip to main content

Detecting BCC's with a SMTP event sink

A couple of weeks ago I blogged this about BCC's and CDOEX, One of the questions that comes up when you start to deal in BCC's is can you detect a BCC programmatically for instance in a anti-spam event sink or if you are worried about confidentiality in an email that was sent. The answer is kind of. For instance you could implement a SMTP event sink on your forward facing Exchange /SMTP box that could detect if a email comings into your organization was being BCC to anyone in your domain. You do this by using the http://schemas.microsoft.com/cdo/smtpenvelope/recipientlist envelope field. This field will contain a list of all the recipients of a message that was submitted by the client (or sending mail server) before expansion of the address has been performed (or categorization in Exchange speak). On a inbound message this would only be the recipients that where in your domain that the SMTP server could deliver to. If you where to compare the recipientlist to the to and cc fields of the message and find any address's that are on the recipeintlist but not in the to and cc fields then you most probably have a BCC. Here's a sample on_arrival sink that would do this

Sub ISMTPOnArrival_OnArrival(ByVal Msg, EventStatus )
on error resume next
Dim RecpList
recplist = LCase(Msg.EnvelopeFields("http://schemas.microsoft.com/cdo/smtpenvelope/recipientlist"))
recparray = split(recplist,";",-1,1)
Set fso = CreateObject("Scripting.FileSystemObject")
set wfile = fso.opentextfile("d:\RECPT.txt",8,true)
for i = lbound(recparray) to ubound(recparray)
if instr(msg.to,replace(recparray(I),"smtp:","")) then
else
if instr(msg.cc,replace(recparray(I),"smtp:","")) then
else
wfile.writeline("BCC Detected " & recparray(I))
end if
end if
next
wfile.close
set wfile = nothing
End Sub

Now this would also work on outgoing mail by finding any BCC's that weren't from your own domain (which would have probably been delivered and removed from the recipientlist). The place that this falls down is it doesn't detect BCC's that wheren't sent to another domain. Say if the message had been sent to you and BCC'd to a yahoo or hotmail account the Recipeintlist won't contain entries for the yahoo or hotmail account. (this would be different if the mail was going outbound from your server where it would contain those entries.)

Popular posts from this blog

The MailboxConcurrency limit and using Batching in the Microsoft Graph API

If your getting an error such as Application is over its MailboxConcurrency limit while using the Microsoft Graph API this post may help you understand why. Background   The Mailbox  concurrency limit when your using the Graph API is 4 as per https://docs.microsoft.com/en-us/graph/throttling#outlook-service-limits . This is evaluated for each app ID and mailbox combination so this means you can have different apps running under the same credentials and the poor behavior of one won't cause the other to be throttled. If you compared that to EWS you could have up to 27 concurrent connections but they are shared across all apps on a first come first served basis. Batching Batching in the Graph API is a way of combining multiple requests into a single HTTP request. Batching in the Exchange Mail API's EWS and MAPI has been around for a long time and its common, for email Apps to process large numbers of smaller items for a variety of reasons.  Batching in the Gr...
Read more

Exporting and Uploading Mailbox Items using Exchange Web Services using the new ExportItems and UploadItems operations in Exchange 2010 SP1

Two new EWS Operations ExportItems and UploadItems where introduced in Exchange 2010 SP1 that allowed you to do a number of useful things that where previously not possible using Exchange Web Services. Any object that Exchange stores is basically a collection of properties for example a message object is a collection of Message properties, Recipient properties and Attachment properties with a few meta properties that describe the underlying storage thrown in. Normally when using EWS you can access these properties in a number of a ways eg one example is using the strongly type objects such as emailmessage that presents the underlying properties in an intuitive way that's easy to use. Another way is using Extended Properties to access the underlying properties directly. However previously in EWS there was no method to access every property of a message hence there is no way to export or import an item and maintain full fidelity of every property on that item (you could export the...
Read more

EWS-FAI Module for browsing and updating Exchange Folder Associated Items from PowerShell

Folder Associated Items are hidden Items in Exchange Mailbox folders that are commonly used to hold configuration settings for various Mailbox Clients and services that use Mailboxes. Some common examples of FAI's are Categories,OWA Signatures and WorkHours there is some more detailed documentation in the https://msdn.microsoft.com/en-us/library/cc463899(v=exchg.80).aspx protocol document. In EWS these configuration items can be accessed via the UserConfiguration operation https://msdn.microsoft.com/en-us/library/office/dd899439(v=exchg.150).aspx which will give you access to either the RoamingDictionary, XMLStream or BinaryStream data properties that holds the configuration depending on what type of FAI data is being stored. I've written a number of scripts over the years that target particular FAI's (eg this one that reads the workhours  http://gsexdev.blogspot.com.au/2015/11/finding-timezone-being-used-in-mailbox.html is a good example ) but I didn't have a gene...
Read more
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.