Event ID - 51

Event Id51
DescriptionAn unknown MTA has attempted to bind. The MTA name in bind is <REMOTE MTA NAME>. The MTA presentation address is /t:0x44454D4F/n:0x444545392D5443504950, Association index: 2018. [MTA XFER-IN 35 42] (14)
Event InformationIf a Session Selector (S Sel) is defined for an X.400 connection defined with X.410 conformance, communication to foreign X.400 systems may not work properly 

Exchange Server incorrectly allows a configuration that sends and expects to receive a Session Selector (S Sel) on an X.410 conformant connection if defined to do so in the X.400 Connector Stack property pages. 

The following is taken from the Red Book, X.410, Page 110, Note 2: 
Message handling will not use Session Layer addressing, that is, a session address will not be passed in the Connect SPDU of the Session Layer.

An X.410 conformant connection is configured by choosing 1984 or 1988 X.410 mode in the message transfer agent (MTA) conformance pane of the Advanced property page for the X.400 Connector. 

Exchange should ignore the S Selector value for X.410 conformant connections. 

Exchange Server 5.0
A supported fix that corrects this problem is now available from Microsoft
Reference LinksX.400 Connector Uses Session Selector on X.400 Connections

Exchange MTA Logs NT Event ID 51

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