Sub Which_Account_Number()
'Don't forget to set a reference to Outlook in the VBA editor
Dim OutApp As Outlook.Application
Dim I As Long

Set OutApp = CreateObject("Outlook.Application")

For I = 1 To OutApp.Session.Accounts.Count
    MsgBox OutApp.Session.Accounts.Item(I) & " : This is account number " & I
Next I
End Sub

Sub Mail_small_Text_Change_Account()
'Only working in Office 2007-2016
'Don't forget to set a reference to Outlook in the VBA editor
Dim OutApp As Outlook.Application
Dim OutMail As Outlook.MailItem
Dim strbody As String

Set OutApp = CreateObject("Outlook.Application")
Set OutMail = OutApp.CreateItem(olMailItem)

strbody = "Hi there" & vbNewLine & vbNewLine & _
          "This is line 1" & vbNewLine & _
          "This is line 2" & vbNewLine & _
          "This is line 3" & vbNewLine & _
          "This is line 4"

On Error Resume Next
With OutMail
    .To = "ron@debruin.nl"
    .CC = ""
    .BCC = ""
    .Subject = "This is the Subject line"
    .Body = strbody

    'SendUsingAccount is new in Office 2007
    'Change Item(1)to the account number that you want to use
    .SendUsingAccount = OutApp.Session.Accounts.Item(1)

    .Send   'or use .Display
End With
On Error GoTo 0

Set OutMail = Nothing
Set OutApp = Nothing
End Sub