Exchange 2013: SMTP 421 4.3.2 Service not active
Exchange 2013 has the Managed Availability functions. Among other things, Managed Availability is able to put Exchange services into maintenance mode. This is important, for example, when updates or service packs are installed on Exchange 2013 servers. During the installation of CU3, however, it happened to me that the maintenance mode was not terminated again. Read more
