As some who has suffered through managing a qmail smtp cluster and dealing with DNSBLs, allow me to say just one thing:
Very. Underrated. Comment.
EDIT: if you are working from IPs that may not be clean (and in an IPv4 world thats prob true) many DNSBLs will work with you to remove your ip's from their lists if you are actually nice and polite with them. Just check your IP's before your set up your network so they have a heads up that someone will be on the other end of any complaints.
That has always works for me.
And if you get rejected with your first request, pester them with a follow up saying something like "Hey, I'm, a cloud customer. I don't control the whole IP range. I ask you to reconsider the initial rejection."
That's always worked for me with outlook. Takes a few days (which is why I say do it as soon as you know what your IP range is)
Be nice and polite (from what I understand real humans read that request) be honest with what you have done as of time of writing the requyest and what you are planning to do.
But be persistent with them and they will basically grant you a whitelist unless you start fucking up.
I don't care, from my perspective they're irrelevant. The last person I communicated who used their MX died recently, and otherwise ATT can bite me. But in a fit of annoyance several years ago I did configure my servers to deliver a heartfelt custom 550 response to ATT MXes.
EDIT: https://www.att.com/esupport/postmaster/digital-signature/ checked the AT&T support about delievery. Seems like they do use Yahoo these days.
I'm talking about the ones managed by Synacor, formerly managed by an ATT spinoff with a bland name I can't remember. I still have my notebook logging my (lack of) progress, which happened over several years and involved a bunch of entities - partners and internal spinoffs.
Trust me, I know how to google "att email".
EDIT: As a follow up. I used to have contacts with BlueYonder, Sky and BT All ISP's that used to manager their own email systems but outsourced them to gmail and yahoo so my peronsal contacts within those companies for email have died off. It wasn't a slight on you. just one geek to another trying to help.
All I meant is that I spent entirely too much time researching the web of entities supporting the Death Star's SMTP needs through the last decade, who on Linkedin listing those companies might be attached to the production technical team, etc. At some point I started joking that I knew knew more about their corporate structure than anyone not suing them or working in their legal department.
I ended up subscribing to an SMTP service that explicitly masked my home IP as Google's sending service included it and was causing my emails to my bank to automatically get flagged as spam.
HN discussion from when they downgraded the free tier, includes some discussion of alternatives: https://news.ycombinator.com/item?id=22192543
Link from the email they sent: https://help.mailgun.com/hc/en-us/articles/360048661093-How-...
DigitalOcean, OVH and Hetzner are especially difficult. It is possible to run an email server there, but getting the IP reputation up will be a tedious process and some providers will simply reject sent emails simply for using one of those hosts.