EWS: Add userproperties to an EML when saving it? - outlook

Question

In some of my mails, I have stored some userproperties via Outlook...
item.UserProperties.Add("CustID", Outlook.OlUserPropertyType.olText)
item.UserProperties("CustID").Value = custID.ToString
On a Pc (server) without Outlook installed, I want to download mail as EML and store the userproperties (like 'CustID' etc.).
My code for saving the EML:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim service As New ExchangeService(ExchangeVersion.Exchange2013)
service.Credentials = New WebCredentials("my#email.com", "mypsw")
service.Url = New System.Uri("https://outlook.office365.com/EWS/Exchange.asmx")
Dim entryID As String = "00000000C802F40668D27342B788D508E9210A67005DF9A7DEF7194A418C8515031D4262280000E00005DF9A7DEF7194A418C8515031D4262280002A9D18B320000"
Dim id As New ItemId(Convert(service, "my#email.com", entryID))
Dim email As EmailMessage = EmailMessage.Bind(service, id)
Dim ps As PropertySet = New PropertySet(ItemSchema.MimeContent)
email.Load(ps)
Using fileStream = New IO.FileStream("D:\sandbox\_email_test.eml", IO.FileMode.Create)
fileStream.Write(email.MimeContent.Content, 0, email.MimeContent.Content.Length)
End Using
End Sub
Private Function Convert(service As ExchangeService, mailbox As String, entryID As String) As String
Dim originalID As New AlternateId()
originalID.Format = IdFormat.HexEntryId
originalID.Mailbox = mailbox
originalID.UniqueId = entryID 'EntryId retrieved from email in Outlook
Dim altBase As AlternateIdBase = service.ConvertId(originalID, IdFormat.EwsId)
Dim convertedID As AlternateId = DirectCast(altBase, AlternateId)
Dim strConvertedID As String = convertedID.UniqueId
Return strConvertedID
End Function
Is there a way I can store userproperties in an EML? If yes, if I double click the EML to open it in Outlook, can I read back the userproperties from the EML?
Thanks!

Answer 1

User Properties are Mapi/Extended properties which aren't include in the MimeStream of a Message. If you add the properties as X-headers instead then they would be available in the MimeSteam otherwise you would better to export the Message as a MSG file which will give you full fidelity on all MAPI properties. To export as a MSG you will need to use Outlook and maybe look at something like redemption http://www.dimastr.com/redemption/rdo_introduction.htm if you need automation.
Cheers
Glen