I have 3 servers and 3 IP's.

Server 1 - Static IP -
Server 2 - Static IP -
Server 3 - Dynamic IP - 333.333.333.333

Now Server 3 is always assigned the IP 333.333.333.333 because it's the only one left, the two others are, as shown above, static to the two other servers.

Is there any reason to assign Server 3 a static IP in regards of "credibility" to the "outside world" (Such as in terms of SMTP / Server credibility) despite the server always have and will be identified by the same IP?

Are there other reasons to give Server 3 a "static IP"?

This is not about SPF / DKIM / Reverse DNS, I'm very well aware of these things and they have been configured. - The question is not about getting unblocked.

  • I think this is basically a duplicate of serverfault.com/questions/48428/… Commented Jan 5, 2016 at 10:18
  • @BlueCompute The issue is not SPF / DKIM, I'm very well aware of these things, my issue lies with the Static / Dynamic IP.
    – Epodax
    Commented Jan 5, 2016 at 10:20
  • Your issue is getting blocklisted, no? You have to take that up with whoever maintains the RBL, we can't de-list you from here you know Commented Jan 5, 2016 at 10:22
  • @BlueCompute The "issue" yes, the question, No. Putting it rather simple "Does a dynamic IP affect SMTP credibility or general server credibility"
    – Epodax
    Commented Jan 5, 2016 at 10:24
  • 1
    To answer your question: If the RBL provider believes that the IP is a dynamically assigned public IP then you will get blocklisted, but you know this because it's happening.... Commented Jan 5, 2016 at 10:32

1 Answer 1


Usually many RBL's will block dynamic ranges from ISP'S, no matter if actually this dynamic range is being used as static addressing.

As an exmaple, you may look at PBL from Spamhaus: https://www.spamhaus.org/faq/section/Spamhaus%20PBL#183

The PBL is simply a list of all of the world's dynamic IP space, i.e: IP ranges normally assigned to ISP broadband customers (DSL, DHCP, PPP, cable, dialup)

  • The IP isn't listed on the PBL.
    – Epodax
    Commented Jan 5, 2016 at 9:43
  • 1
    Another reason for this is reverse DNS lookups. Have you added a reverse DNS for such an IP?
    – Xavy
    Commented Jan 5, 2016 at 10:10
  • Yes, I have added reverse DNS.
    – Epodax
    Commented Jan 5, 2016 at 10:12
  • 2
    Perhaps worthy if you could mention which provider blocked you and which message which it reported back. It usually gives some clues on the reason of listing. If this happened with MS mail servers (msn.com, outlook.com, etc) you may need to subscribe to their reputation programs (JMRP/SNDS), review their ToS, and request unlisting if fulfulling them
    – Xavy
    Commented Jan 5, 2016 at 10:23
  • Verizon and "because your ISP indicates that it is dynamically assigned"
    – Epodax
    Commented Jan 5, 2016 at 11:03

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