https://answers.microsoft.com/en-us/outlook_com/forum/oemail...
But other than that, running my own mail server hasn't been much of an issue. Set up sendmail, use public blacklists for spam control, and it pretty much runs without any intervention.
I'm thinking of solving it by blacklisting outlook.com domain, so that senders at least know that I can't respond to them. I can put a message in the error response, that will be reliably relayed to the sender by the sending system.
Google's slightly better. Recently I did an experiment and created a few gmail accounts and sent some riduculously spammy messages full of typical keywords in between those gmail accounts, and they were all successfully delivered. Always.
Then I sent e-mail from new gmail account to my email server and simply responded and it went to spam. It's ridiculous that such a simple heuristic like someone responding to a message gmail user sends doesn't get the message through spam filters, even though the system can clearly determine taht the message is legit based on many variables (References field referencing message-id of the original message (noone else than the recipient should know this), reply being from a correct source (DKIM/SPF), message having normal looking business content, etc.).
There's way too heavy a weight on sending server IP range reputation.
But gmail was not. Even as a business user with support.
Gmail rejects me as an ugly spammer at the gate when using IPv6 but not when using IPv4.
My IP addresses are not listed in any public blacklists.
And the Borg hivemind is not able to tell me why. Gmail support is friendly but have no knowledge of their filter nor an escalation path.
The amusing part is they reject me as a bulk sender. But when I register into their bulk mailer program my volume is too low.
This is with strict SPF, DKIM, DMARC and registered with dnswl.org.
https://support.google.com/mail/contact/msgdelivery?vid=0-35...
I had a problem with ipv6 myself with gmail, but the problem was that I just didn't have ipv6 fully set up on my server, so either SPF or reverse DNS wasn't working or something like that. I think I just configured sendmail to only use ipv4 and that solved the gmail issue.
This was my experience, too. I took this advice [1] configuring postfix and Gmail started to accept my emails.
[1] https://christian.skala.me/blog/gmail-why-are-you-doing-this...
https://support.google.com/mail/contact/msgdelivery?vid=0-35...
Mail server setup for the uninitiated does look a little daunting, especially if you're more accustomed to "all-in-one"-ish software. If you want to do this, I recommend starting with making sure you have a clear mental model of mail server architecture, especially where it touches other things (DNS, DKIM, spam filters, local delivery, probably IMAP, maybe LDAP, maybe databases, etc.) Without a clear idea of the dataflow and reasons for different decision-points, you're going to have a very bad time troubleshooting things.
[1] SBCGlobal.net has been rejecting me for over a decade despite there being zero spam ever having been emitted by my domain. Eh, my userbase communicates with exactly one SBC user; ATT can bite me.