Maxconcurrentconnectionattempts Option
From MsgServerDocWiki
Introduced in release: 7 Update 3
Number of outstanding connection attempts permitted to the same backend mailstore. If this is exceeded, users on that mailstore will have their connections rejected with a temporary service outage error. This limit prevents a DNS or mailstore outage of one server from consuming all the MMP worker threads.
The default value is: 10

