Si declaras esta API
Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" _
(ByVal hWnd As Long, ByVal lpOperation As String, ByVal lpFile As String, _
ByVal lpParameters As String, ByVal lpDirectory As String, _
ByVal nShowCmd As Long) As Long
no tendrás nada más que ejecutar lo siguiente:
Dim sLink As String
sLink = "direccioncorreo@hotmail.com"
ShellExecute 0, vbNullString, "mailto:" & sLink, vbNullString, vbNullString, vbNormalFocus
Saludos