Big providers often only support their own forms and ignore open sources trust providers.
Small providers often do not maintain their email services which will simply auto spam your mail/domain, when it does not come from the big 10 providers.
* web.de
* gmx.net
I also have to say that I always used a hetzner root server. Moved multiple times due to an upgrade.
I ALWAYS had to manually apply for removal of my Webserver. It worked for Yahoo. At that time it did not work for Gmail and Microsoft. I no longer was blocked but if I was writing for the first time to a recipient, I landed in the spam folder.
The software I used mailinabox and mailcow. Both had self checks. All green. I also used external scanners to check my config, all fine. You can check my GitHub (razemio). I even contributed to some issues for mailinabox.
This is not only true for selfhosting but also small providers. As an example:
* mailbox.org (auto spam Gmail and microsoft 2018)
All of this was a long time ago. Maybe I am just depressed from the bad experience and the FAQs are telling the truth. However it is hard to believe for me.
I am selfhosting since 1997 and I am working in programming / DevOps.
I set up a mail server with NixOS 5 times in a row with 5 different Hetzner Cloud IPs and each of them arrived fine at Google.
Also works for Microsoft services?
> Also works for Microsoft services?
No, Microsoft seems to have an allow-list for servers, and ban everything by default (the laziest of approaches).
But that's OK: Because Microsoft does it so poorly, Microsoft email users check their Spam folder all the time anyway.