Setting the Message-ID of outgoing emails?

[Anonymous]

Is it possible to set a custom message ID for outgoing emails based on data in my leads? 

[Kristen_Malkov1]

Can you explain a bit more about what you mean regarding a 'custom message ID'? What are you trying to accomplish?

[Anonymous]

Referring to controlling this header: http://en.wikipedia.org/wiki/Message-ID

On emails being sent from Marketo. 

[SanfordWhiteman]

Can't imagine any way to do this.  Remember, we don't even have access to the MIME-wrapped form of the message, just the individual HTML and text parts. Customizing SMTP headers is a step beyond that.

Also, Message-IDs need to be globally unique.  What algorithm would you use to guarantee such uniqueness?

But more to the point, as @Kristen M asked, what are you trying to accomplish?  If you're trying to hide information from human readers that can be parsed by a machine, you can do this with an HTML comment.