I’ve been struggling with both Spectrum and Microsoft for about a month or so now, too. I host a small site for a non-proft that I’m part of on a Droplet that I otherwise use for personal hosting. I run a few mailman lists for the organization that we use to send maybe 200 emails/week to our members, if we’re lucky. I’ve been doing this for a few years and have become quite familiar with all the mail-related acronyms: RDNS, SPF, DKIM, DMARK, and everything is in order and the server itself is not blacklisted anywhere that I can find.
With our predominant local ISP being Spectrum (formerly Time Warner), we have lots of members using their RoadRunner email accounts, which was the first ISP where I noticed issues. Unfortunately the error message Spectrum returns is simply “SMTP server unavailable,” which is completely unhelpful, especially when I can send from another (non-DO) email address with no problems whatsoever.
I am a Spectrum customer myself, so I have an email address with which to test. I’ve tried reaching out to support, but I get nowhere. Emails to various postmaster@, ubblock@, etc. addresses either bounce or go unanswered.
What cued me in to where the problem actually lies was when hotmail and outlook.com mail started bouncing. Microsoft provided a bit useful bounce error message indicating that we were blocked because of a wider block on a range of IP addresses. With some searching, I came across this form, and I got an email within less than 24 hours indicating that we were “conditionally unblocked.”
Spectrum is still an issue. I’m now thinking that I may move the non-profit’s site onto a server I have with a different host to see if that makes a difference. I don’t want to do that as the DO server has better resources, but not being able to send email to Spectrum, as much as I want to tell all of our members to switch to something better, is a real deal breaker. We have no real budget for web/email services, so going to a dedicated email provider really isn’t an option for us.