All Messaging Gateway (SMG) version 10.6 releases reached end of support life (EOSL) in May 2019.
SMG 10.6 was released at the end of November 2015 and exceeded its four year support lifespan in May of 2019.
Please see the Product Lifeycle tab of the Messaging Gateway product support page for definitive end of service (EoS) dates for the SMG product.