Office 365, Exchange Online, has a feature where it downloads emails from a third party account through POP. The problem that I'm experiencing is that with Outlook, both 2013 and 2016, it sends as the address it was sent to, not the address the main address. In this case, the problem is that the user is getting AOL.com emails through this mechanism, and when they reply, it bounces because AOL has a DMARC record in place that prevents other systems, Office 365 in this case, from sending on behalf of an aol.com. Let me be clear that this is a case of sending "on behalf of," not sending as. When received it would read something like "From johndoenewdomaincom on beahalf of johndoeaol.com." AOL is blocking this. I have spoken with Office 365 support and they offer no resolution.

I have taken note of properties of a new email that appear to be different when sending using the connected account and created a macro to clear them, which is how they appear to be in a normal email. However, when I send it, it either sends but is never received, with Outlook in cached Exchange Mode, or it stays in the Outbox, in online mode. I have to believe that there is a property that I am missing, but I don't see anything else. Below is my macro, any help would be appreciated.

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
    
    Dim olNS As Outlook.NameSpace
    Set olNS = Application.GetNamespace("MAPI")
    Dim oAccount As Outlook.Account
    Set oAccount = olNS.Accounts.Item(1)
    
    Item.SentOnBehalfOfName = Empty
    Item.Sender = ""
    Set Item.SendUsingAccount = oAccount
    Item.ReplyRecipients.ResolveAll
    Item.Save  
    
End Sub