Dim contactfolder As Outlook.MAPIFolder = ol.ActiveExplorer.Session.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderContacts)

Dim emails = From email In inbox.Items.OfType(Of Outlook.MailItem)() Select email
Dim contacts = From contact In contactfolder.Items.OfType(Of Outlook.ContactItem)() Select contact

Dim emailswithcompany = From email In emails Join contact In contacts _
    On email.SenderEmailAddress Equals contact.Email1Address _
    Select email, contact.CompanyName

For Each emailwithco In emailswithcompany
    Debug.Print(String.Format("{0} from {1}: {2}", _
       emailwithco.email.SenderName, emailwithco.CompanyName, emailwithco.email.Subject))
Next

This worked fine. I got a list of the sender and subject from the emails and company names from the contact records.

Then I queried the database and did a JOIN with the above results. It was funny to see how the types and subtypes kept growing as I built this up in layers. It's nice to have things organized, but if I were starting from scratch, I might do this a bit differently so that my resulting types aren't so complex*.

Dim awdc As New awlinqDataContext
Dim custSalesPerson = From cust In awdc.AWCustomers Select cust.CompanyName, cust.SalesPerson
Dim emailswithcompanysp = From emailco In emailswithcompany _
   Join cust In custSalesPerson _
   On cust.CompanyName Equals emailco.CompanyName _
   Select emailco, cust.SalesPerson

For Each emailwithcosalesp In emailswithcompanysp 
  Debug.Print(String.Format("{0} from {1}: {2}" & NewLine & "SalesPerson:{3}", _
    emailwithcosalesp.emailco.email.SenderName, _
    emailwithcosalesp.emailco.CompanyName, _
    emailwithcosalesp.emailco.email.Subject, _
    emailwithcosalesp.SalesPerson))
Next

And voila!

Now I could write an app that can distribute email to the correct sales people when they come into a general mail box! Well, I supposed I could have done it prior to having LINQ (or maybe in Exchange which I know nothing about), just with a lot more effort!

*I couldn't resist streamlining the final solution.

Dim ol As Outlook._Application = New Outlook.Application
Dim inbox = ol.ActiveExplorer().Session.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox)
Dim contactfolder As Outlook.MAPIFolder = ol.ActiveExplorer.Session.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderContacts)
Dim emails = From email In inbox.Items.OfType(Of Outlook.MailItem)() Select email
Dim contacts = From contact In contactfolder.Items.OfType(Of Outlook.ContactItem)() Select contact
Dim awdc As New awlinqDataContext
Dim custSalesPerson = From cust In awdc.AWCustomers Select cust.CompanyName, cust.SalesPerson

'now query across emails, contacts and custSalesPerson in one query