[ixs]

What I find so baffling is that these experiences do not match my own at all.

I've been running a non-profit ISP for about 23 years with a few friends. We've always been doing this from our own IP Space (/20) in RIPE. Even when we had problems sending spam (compromised user accounts, compromised php websites) and we ended up on a blacklist, we usually could get removed pretty fast.

For a few years our mail system would sometimes generate late-bounces, that is accept a mail on the incoming MX only to then figure out that it actually cannot be delivered later on and generate a delivery failure notification mail. Not a good situation.

That got us into some trouble here and there. But even that could easily be unblocked again.

When we finally managed to set up a new mail infrastructure (2 year project cause it's a hobby) we set up new outgoing SMTP servers which cycle through multiple IP addresses. There was exactly one ISP (Deutsche Telekom T-Online) that was not accepting mail from some of these IPs. One mail and a turnaround time of abour 12hrs later this was fixed. Gmail or Hotmail/live.com/Outlook never had any problems with deliverability. Even with a few users forwarding all their email to their gmail accounts including the spam that slips through our filters. That might mean that a single mail would not be deliverd, but other users never suffered as our outgoing IPs are not being blanket-banned.

There's one residential ADSL provider that has a blanket ban on one of our outgoing IPs. There's no way to get that resolved because their mail infrastructure is unmaintained and nobody is reading their mail. Common problem with that one ADSL provider, googling their name shows other people have the same problem. shrug We just use a different outgoing IP for them.

No DMARK or DKIM setup at all for outgoing mail.

So I wonder, what really makes the difference in experience? Is it just the fact that we have a decent sized IPv4 Network in our name as PI space?