[jonathanstrange]

What the original poster describes is anti-competitive behavior, for this reason alone the idea of blocking the whole IP range of a competing email service provider is very bad. Personally, I wouldn't use an email provider that blocks spam server-side without an option to turn this off because these filters often block legitimate mails and can cause all kinds of annoying problems.

[literalAardvark]

Kind of, but parent poster was talking about his own small server, which is likely hosted on a residential IP pool that's pretty much guaranteed to be blocked all the time.

All mail providers mass block IPs, because the spam from some ISPs is literally too much to even filter.

I run a few high volume (very legitimate) servers and it's been a huge pain in the butt to keep them off of blacklists, but at the same time we've also had spammer problems and I totally get it.