Event ID - 146

Event Id146
SourceMSExchangeMTA
DescriptionAn attempt to route message <message id> to recipient <recipient> (recipient number: <value>) failed because the specified recipient is ambiguous. [<value> <value> <value> <value>] (14)
Event InformationVerify that the recipient is valid and has a unique address. Use Network Monitor to capture Network Traces, then view these traces from Network Monitor for any network issue. If the error persists, stop and restart the message transfer agent (MTA) service
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