... very curious to know what this sysop considers a "serious mail provider."
A serious mail provider would care about ensuring that this does not happen and handle enquiries sent to the RFC-mandated address postmaster@ and respond promptly to such enquiries.
I might have ignored email complaining about delivery issues if the above wasn't handled if I were running a serious email provider.
To this day is too much effort running your email service. I moved to an account to Infomaniak that works good and I don't dove all my data to Microsoft or Google.
That's why I meant the above as table stakes. They are the cost to even get in the game to get punched with bullshit IP reputation lists.
But if one doesn't have even PTR records, one has no leg to stand on complaining about blocklists.
I send lots of email that is verified with SPF and DKIM to them via relays. But any messages sent directly from "untrustworthy" IP ranges are just blocked with a generic message.
This is in contrast to GMail which rightfully treated my first messages as suspicious. But once a handful of users pressed "not spam" they don't care about what IP it comes from anymore as the domain reputation has taken precedence.
As others have mentioned, the domain also does not use SPF, DMARC or PTR address. So it'll also be unlikely that they sign their outbound email with DKIM.
And they suck.
> permanent error (550): 5.7.1 Unfortunately, messages from [{REDACTED IP}] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
The other providers don't seem to be as picky. (At least I haven't seen major issues sending from Digital Ocean which is an ASN with a bad reputation.) It seems that once they had experience with my domain (with SPF + DKIM) they judge messages primarily using domain reputation not IP reputation.
Simply said: if block lists were permanent, we'd be blocking the entire IPv4 space by now. And also, spammers would have almost free reign when using IPv6, since you can get blocks of millions of addresses for free. Large email providers know this, they have been battling spam for decades now.
When enabling DMARC the IP address more or less becomes irrelevant. If the email is not DMARC aligned the email won't be accepted anyway (I'm assuming a 'reject' DMARC policy here) and if the email is DMARC aligned, the domain reputation, rather than IP reputation will be used.
When working with DMARC aligned domains, most email service providers will rely solely on content based spam detection, and how often people flag the email as spam to determine the domain's reputation.
Of course I am generalizing here. What I wrote here is true for most large email service providers, but each have their own implementation. And of course there will always be self-hosted/on-premise solutions that keep using static block lists (for example: Spamhaus).
> When working with DMARC aligned domains, most email service providers will rely solely on content based spam detection
This seems to be true for most major providers. But my experience shows that Microsoft and Apple don't do this. They still apply strict broad IP-based blocking. Sending messages from the same domain via a relay such as AWS SES is perfectly fine. But if the sender IP is in Digital Ocean ASN it is dropped right away. The domain is p=reject
He had manually added over 20,000 IP addresses to the list.
Come on, I have DKIM and SPF on my "just send sign-up and password reset emails" domains...
Eventually I find a portal from MS to do exactly that: Appeal. I tried to use the portal but I got an error "event service error" - or something similar. Portal not working. I say "what the heck - I ll try later". I do try later, same outcome. Several times. For days. I google the error, I find several threads on redit since years complaining that the portal doesn't work giving this exact error. Since years. I keep trying nevertheless to respond to the email and go through the portal again for days. Nothing. I try the following: I signup for azure, it asks me for an email address, I say I have none and guides me to sign up to outlook. Outlook asks me for a backup email address, I provide my email address from the blocked server.
I then try to respond again to the original email that outlook has been rejecting - WORKS. Summary again: MS blocks email my mail server for not fulfilling requirements that it actually fulfills. MS portal to object, doesn't work since years. I create an outlook email and set self-hosted mail address as "backup" - my server gets unblocked.
Fun fact: I received "on-boarding" emails from MS Azure to my new MS Outlook account. MS Outlook classified them as "Junk".
Does this qualify as a "serious mail provider"?
--updated wording.
This is all assuming that the mail is otherwise ticking all the boxes. One too many times I’ve seen someone get on their HN soapbox because their $5 DigitalOcean mail server keeps getting shit-canned, only to find after some polite prodding that they just flat-out weren’t aware of the modern-day complexities of sending email.
Not to say that this is what’s happening here, of course.
No SPF, DKIM, DMARC records. No PTR record for their A address.