I have an odd experience here. I have had loads of problems embedding a logo or image to emails using the src=cid... found out it wont show if not setting size for example.<
You need to set PR_ATTACH_CONTENT_ID property (DASL - http://schemas.microsoft.com/mapi/proptag/0x3712001F) on the attachment using Attachment.PropertyAccessor. Be aware, the PropertyAccessor property of the Attachment class was added in Outlook 2007.
You may find the How do I embed image in Outlook Message in VBA? link helpful.
Just to post the simple form of code that works. Big thanks to @Eugene Astafiev.
Sub test()
Dim oApp As Outlook.Application
Dim oEmail As MailItem
Dim colAttach As Outlook.Attachments
Dim oAttach As Outlook.Attachment
Dim olkPA As Outlook.PropertyAccessor
Const PR_ATTACH_CONTENT_ID = "http://schemas.microsoft.com/mapi/proptag/0x3712001F"
'create new Outlook MailItem
Set oApp = CreateObject("Outlook.Application")
Set oEmail = oApp.CreateItem(olMailItem)
'add graphic as attachment to Outlook message
'change path to graphic as needed
Set colAttach = oEmail.Attachments
Set oAttach = colAttach.Add("C:\temp\logo.jpg")
Set olkPA = oAttach.PropertyAccessor
olkPA.SetProperty PR_ATTACH_CONTENT_ID, "logo.jpg"
oEmail.Close olSave
'change the src property to 'cid:your picture filename'
'it will be changed to the correct cid when its sent.
oEmail.HTMLBody = "<BODY><IMG src=""cid:logo.jpg""> </BODY>"
oEmail.Save
oEmail.To = "someemail@gmail.com"
oEmail.Subject = "test"
oEmail.Send
Set oEmail = Nothing
Set colAttach = Nothing
Set oAttach = Nothing
Set oApp = Nothing
End Sub