Fair questions to ask! I can’t remember the exact site I found the statistics on, but I saw some charts that aligned with my personal experience. It showed the rate of IPs under certain ASNs being blocked by mail servers. VULTR (Choopa) was at the top (want to say it was like 80%ish), which makes sense because they have some of the cheapest prices and are therefore more economically accessible to abusers.
I’ve also found that my emails often get blocked by major networks (Gmail, Office 365 / Outlook.com, haven’t tried Yahoo). These lists are internal to them and (afaik) not queryable, which is why the typical checker sites wouldn’t see any records of you being blacklisted.
Microsoft specifically emailed me a reply when my message was blocked, returning as part of the message 550 5.7.1 Service unavailable; Client host [104.156.252.162] blocked using FBLW15; To request removal from this list please forward this message to delist@messaging.microsoft.com (in reply to RCPT TO command)
Gmail also blocks me, but not for any reason that I can tell. The spam headers show nothing, and the return code is successful delivery, so there’s something else going on on Gmail’s end that’s filtering my server, and I’m very confident it’s IP reputation.
As I understand it, FBLW15 is a massive list of denials for specific providers that have had significant abuse in the past. I could totally be wrong, and I’m open to accepting that if I am.
To get removed from these lists:
Google has a “feedback loop” that you can join, though I think it’s targeted mostly for mass mailers, but there’s nothing better for personal servers, so it’s really the only option I know of. Applying for the feedback loop and delisting is rather annoying, hence why I haven’t completed it yet.
Microsoft lets you reply to the error email they send you when you’re blocked, which opens a ticket with MS support, and they remove you.
I don’t know about Yahoo.
To recap:
- I have valid SSL certs, with the good MIAB configuration settings enabled.
- My DKIM, DMARC, and SPF records are set correctly
- My PTR record is set correctly
- I have valid WHOIS info
- I do not send mass mail… at all.
- Various spam/blacklist test sites show no issues
- I’m on DNSWL.org
- I’m not on any queryable blacklists
There’s no tangible reason for me to be blocked, but I have been since day 1, which really leads me to believe, as the aforementioned site showed, that a lot of VULTR’s ASN was blocked.