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Error 442: No delivery mechanism available
Technical Articles ID:   KB60427
Last Modified:  2/23/2017


McAfee Email and Web Security Appliance software 5.x


When sending outbound email to the Internet through an Email and Web Security Appliance, they are immediately placed in the Email Queue. When attempting a real time retry of the message, you see the following error message:
ERROR 442: No delivery mechanism available


The MX Record for the remote domain is incorrect or does not exist.


An MX Record can be interrogated by performing an NSLOOKUP as follows:
nslookup -type=mx domain.com

An invalid result shows as follows:

Non-authoritative answer:
domain.com mail exchanger = 10 

A valid MX record shows as follows: 
non-authoritative answer:
domain.com mail exchanger = 10 mail.domain.com.
mail.domain.com  internet address =

As per RFC 1035 Section 3.3.9. (MX RDATA format), the MX record format must be as follows:

  • PREFERENCE: A 16-bit integer which specifies the preference given to this Reverse Record among others at the same owner. Lower values are preferred.
  • EXCHANGE: A <domain-name> that specifies a host willing to act as a mail exchange for the owner name.
  • MX records cause type A additional section processing for the host specified by EXCHANGE. The use of MX Reverse Records is explained in detail in [RFC-974].

IMPORTANT: This Appliance behavior is in compliance with the RFC.

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Affected Products

Email & Web Security 5.6

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