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3559 Views 2 Replies Latest reply: Jan 29, 2014 1:36 PM by lpullen RSS
pcgnow Newcomer 1 posts since
Jan 8, 2013
Currently Being Moderated

Jan 8, 2013 3:54 PM

451 All MX servers are unavailable for domain

Anybody else seen this error on outbound messages? 451 All MX servers are unavailable for domain


Several of our users are experiencing problems when sending to They get the message bounced back. Others are fine and able to deliever. So it seems hit or miss and has been happening over the last three days or so.


The knowledge base indicates the error as the following:


This error indicates that all MX servers were unreachable for the destination. If you are receiving this error sending mail TO a domain, please verify that DNS servers are reliably responding.


Please note that if DNS servers are intermittently failing, the verification you perform at that moment may not be indicative of the performance at the time the message was sent.


If this error has happened when mail was being sent TO your domain filtered by the McAfee service, this indicates that we are not able to reach your Inbound Server. Please confirm the destination server is reachable or engaged your Disaster Recovery service.



Am I wrong in thinking that if there is a DNS problem that needs to be verified and corrected that it would be McAfee's DNS servers or Comcast's MX records?


I have opened a ticket with support, but I am curious if anyone else has seen this with either comcast or other domains?






  • Brad McGarr McAfee Employee 154 posts since
    Dec 4, 2012

    Greetings pcgnow,


    We had an issue late yesterday and early today where Comcast had one or more McAfee IPs on their blacklist. Our operations team was able to work with Comcast to get those removed, and everything should be working fine now. Those errors are temp-fails, so the messages will be retried for up to 5 days.


    Have a great day!

    Brad McGarr
    McAfee SaaS Email & Web Protection
    Technical Support Technician I (Legacy & Partner Support)
    Microsoft Certified Professional
    Microsoft Technology Associate - Windows OS | CompTIA A+ Certified Technician | CIW Web Foundations Associate
    Visit my blog: Brad's Corner - Insights from SaaS Email & Web Security Support

    Frequently Requested Information
  • lpullen Newcomer 7 posts since
    Jan 29, 2014

    We are still seeing this issue with Time Warner.  More specifically and addresses.


    Recipient Disposition: [250 Queue (RCPT Domain, Message Domain; Mode: ; Queued: yes; Frontend TLS: yes]
    Detail: first attempt failure: 451 all mx servers are unavailable for domain

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