Macro to create email, and pick which email account to send from

I already have this set up how I want...

Sub MakeMsg()
Dim msg As Outlook.MailItem
Today = Format(Now(), "mm-dd-yy")
Set msg = Application.CreateItem(olMailItem)
With msg
.To = "XXXX@XXX.com"
.Subject = Today & " Subject Line"
.Display
End With
End Sub

What I can't figure out is how to pick which email to send from.
I have several emails in my outlook, but when the Macro is run, it defaults to the wrong email.

How can I go about changing this?

--Thanks