Reference: Suddenlink, Optonline, Cablevision Email Domains

Cablvevision, Optonline, and Suddenlink cable internet services all seem to be owned by Altice USA, a company spun out from the European telecommunications provider Altice.

This seems to be a company cobbled together from multiple acquisitions so it's not clear if the inbound email services are all run the same way across what used to be different legacy providers. Nonetheless, if you're looking to set throttle settings or connection limits, it couldn't hurt to group these together as a single ISP, with the assumption that they are likely to have similar recommended settings across the board.

This list may be incomplete, but it's probably relatively comprehensive, based on MX record checking over time.

Cablvevision, Optonline, and Suddenlink Email Domains:,,,,,,,,,,,,,,,,,,,,

On a related note, this ISP or group of ISPs seem to be one of the most difficult to contact about deliverability issues. Emails to postmaster are rejected, and there's no postmaster site or contact form to be found. I hope they'll notice this and consider publishing a contact path in the future, as it can be very frustrating for senders to deal with. (Or if you don't want to deal with it, outsource the whole thing to somebody with a remediation process, like Vade, Cloudmark, or Proofpoint.)


Comments policy: Al is always right. Kidding, mostly. Be polite, please and thank you.

  1. Suddenlink's inbound is built upon Openwave MTAs (now Synchronoss), where as most of the other domains use Cloudmark MTAs for inbound. Treating them all the same might not be a good idea. From what I've heard the Cloudmark installations are outdated and they haven't ponied up for updating their licenses. Cloudmark has no control over these installations and can't help from a deliverability perspective.

  2. That's good intel. Thank you for sharing! Separate mail infrastructure, with one side of it seemingly not well supported suggests some consolidation might be in their future. We'll see how it shakes out!

  3. I believe the optimum/optonline, etc. domains are part of Spectrum now (along with Roadrunner).

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