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Knowledge Base

Email Security: How to troubleshoot NDR's.

Description

Email Security: How to troubleshoot NDR's.

Resolution

Question:

I do not receive NDR's, How can I see what a message was rejected?

Troubleshooting:

In Email Security go to the System > Advanced Page and download the MTA hourly log for the time the original message was sent.

Keep in mind that these are logged in GMT so you will need to add hours according to the time zone you are in.

Listed below is the general ESMTP response codes you may see listed in an SMTP conversation.

ESMTP STATUS CODE

DESCRIPTION

211

System status, or system help reply

214

Help message
(Information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user)

220

Service ready

221

Service closing transmission channel

250

Requested mail action okay, completed

251

User not local; will forward to

354

Start mail input; end with "."

421

Service not available, closing transmission channel
(This may be a reply to any command if the service knows it must shut down)

450

Requested mail action not taken: mailbox unavailable
(E.g., mailbox busy)

451

Requested action aborted: local error in processing

452

Requested action not taken: insufficient system storage

500

Syntax error, command unrecognized
(This may include errors such as command line too long)

501

Syntax error in parameters or arguments

502

Command not implemented

503

Bad sequence of commands

504

Command parameter not implemented

550

Requested action not taken: mailbox unavailable
(E.g., mailbox not found, no access)

551

User not local; please try <....>

552

Requested mail action aborted: exceeded storage allocation

553

Requested action not taken: mailbox name not allowed
(E.g., mailbox syntax incorrect)

554

Transaction failed

For specific codes for Microsoft Exchange please see their KB: http://support.microsoft.com/kb/284204

There are also many other documents in the Microsoft KB depending on the NDR you are seeing.

Resolution/Workaround:

  • Depending on the type of Email Server you use and the type of server your sending to you may see different messages.
  • However the numbered code will always be the same on an NDR.
  • BATV (Bounce Address Tag Validation) can also cause an NDR and Out of Office replies to not be recieved.
  • BATV will drop an NDR or Out of Office reply if the mail from address is a NULL value.
  • Note: Exchange settings prevent an NDR or a Out of Office reply from using the original recipients email address in the mail from field and will alter to a NULL value if it is destined for outside of the local network.
  • The only fix's for this and to be able to get NDR's or Out of Office replies would be to either alter the default behavior of the Email Server or to turn off BATV.
  • If BATV is turned off and you still do not get any NDR's or Out of office replies then it may be possible that an internal MX and A record does not exist on your internal DNS server for your own domain.
  • The MTA does MX record routing, so when an NDR is generated by the local outbound MTA to the original sender the MX lookup returns the public IP address to route to.
  • Depending on firewall settings these will not be returned to the internal email server unless a local record exists to point to the internal email server or a look back policy is set in the firewall to direct the SMTP traffic destined for the public IP of the MX record back to the internal mail server private IP address.