CAS server NLB cluser


  • Dear all,

    in my organisation we have 2 cas, 2 mbx servers. 
    2 cas servers are in nlb cluster, and use one unique ip adress.

    Internal and public DNS and ASA firewall is setup to target/nat to nlb cluster unique ip adress.

    And when I send mails to live or gmail service, mails goes to spam. In header of mail I saw that mails doesnt go trough fixed public ip adrees, mail goes trough public ip adrees for internet browsing.

    Tuesday, December 20, 2016 2:56 PM

All replies

  • Hi.

    1. Please check A and MX record for all IP address.

    2. Please check SFP and PTR records for IP and name for email system.

    Understanding SMTP Failover and Load Balancing in Transport

    Set up SPF in Office 365 to help prevent spoofing

    MCITP, MCSE. Regards, Oleg

    Tuesday, December 20, 2016 3:38 PM
  • NLB is usually an "incoming" technology, not "outgoing" (like send connectors). Is the gateway on your NLB adaptors? you shouldnt use NLB with port 25, use smart hosts.
    Tuesday, December 20, 2016 3:42 PM
  • Hi,

    You are trying to send mails directly through your internet IP, and the IP may have already under listed in spam (check with Even if you de-list your IP from spam, it will come again under spam list. And this is normal that the public IP is in the mail header.

    I suggest to first check with your ISP, if they can provide you a mail gateway or use any mail gateway device in your network. Or send mail through any smarthost (any mail service provider). There are very cheap smarthost provider available in market even under twenty dollar a month. 


    • Edited by PK Sarangi Tuesday, December 20, 2016 4:08 PM
    Tuesday, December 20, 2016 4:07 PM
  • Or use smart host 

    or you can EOP or any other 3rd party solution to route your email externally.

    Where Technology Meets Talent

    Tuesday, December 20, 2016 9:53 PM
  • can you copy paste the error log , under Exchange log in event viewer 

    Where Technology Meets Talent

    Wednesday, December 21, 2016 5:09 AM
  • Hi,

    According to your description, I understand the mails go to Spam when sending to live or Gmail domain.

    I will ask some related questions for better analysis.

    Have you received any error message when failed to send emails?

    Whether you can send emails fine to other external domain?

    Do you check if your domain/ ip is on blacklist here: ?

    Best Regards,
    David Wang
    TechNet Community Support

    Please remember to mark the replies as answers if they helped.
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    Monday, December 26, 2016 7:53 AM