An attempt to route message {message id} to recipient {recipient} (recipient number: {value}) failed because the specified recipient is ambiguous. [{value}{value}{value}{value}] (14)

Details
Product:	Exchange
Event ID:	146
Source:	MSExchangeMTA
Version:	6.0
Component:	Message Transfer Agent
Symbolic Name:	MTA00146
Message:	An attempt to route message {message id} to recipient {recipient} (recipient number: {value}) failed because the specified recipient is ambiguous. [{value}{value}{value}{value}] (14)

User Action
Verify 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. If the error still persists, restart Microsoft Exchange Server.