align=”center” style=”background:#f0f0f0;” ’'’First digit:’’’
  2.x.x successful transfer  
  4.x.x persistent failure  
  5.x.x permanent failure  
  align=”center” style=”background:#f0f0f0;” ’'’Second and Third digits:’’’
  x.1.0 other address status  
  x.1.1 bad destination mailbox address Example: 5.1.1 [[Bounce when Sending Meeting Request (Outlook)]]  
  x.1.2 bad destination system address  
  x.1.3 bad destination mailbox address syntax  
  x.1.4 destination mailbox address ambiguous  
  x.1.5 destination mailbox address valid  
  x.1.6 mailbox has moved  
  x.1.7 bad sender’s address syntax  
  x.1.8 bad sender’s system address  
  x.2.0 other or undefined mailbox status  
  x.2.1 mailbox disabled, not accepting messages. See: [[Bounce 5.2.1 when emailing a public folder (Exchange)]]  
  x.2.2 mailbox full  
  x.2.3 message length exceeds administrative limit  
  x.2.4 mailing list expansion problem  
  x.3.0 other or undefined mail system status  
  x.3.1 mail system full  
  x.3.2 system not accepting network messages  
  x.3.3 system not capable of selected features  
  x.3.4 message too big for system  
  x.4.0 other or undefined network or routing status  
  x.4.1 no answer from host  
  x.4.2 bad connection  
  x.4.3 routing server failure  
  x.4.4 unable to route  
  x.4.5 network congestion  
  x.4.6 routing loop detected  
  x.4.7 delivery time expired  
  x.5.0 other or undefined protocol status  
  x.5.1 invalid command  
  x.5.2 syntax error  
  x.5.3 too many recipients  
  x.5.4 invalid command arguments  
  x.5.5 wrong protocol version  
  x.6.0 other or undefined media error  
  x.6.1 media not supported  
  x.6.2 conversion required and prohibited  
  x.6.3 conversion required but not supported  
  x.6.4 conversion with loss performed  
  x.6.5 conversion failed  
  x.7.0 other or undefined protocol status  
  x.7.1 delivery not authorized, message refused  
  x.7.2 mailing list expansion prohibited  
  x.7.3 security conversion required but not possible  
  x.7.4 security feature not supported  
  x.7.5 cryptographic failure  
  x.7.6 cryptographic algorithm not supported  
  x.7.7 message integrity failure  

==See Also== [http://support.microsoft.com/kb/284204 Delivery status notifications in Exchange Server and in Small Business Server (Microsoft Support)]
[http://www.napolifirewall.com/NondeliverableReport.htm Exchange NDR Codes]