Earlier quoted context omitted.
My ISP doesn't block port 25, but since my IP address is technically dynamic, it's on Spamhaus' Policy Black List. That said, my ISP offers SMTP servers for proxying outgoing messages, so I used that for a while. I switched to a VPS because my home server died.
Gotta love that Spamhaus logic. Spammers use cheap dynamic IP's therefore anyone with a cheap dynamic IP that sends an email is a spammer. Is it cheaper for you to get a static IP from a VPS than from your ISP?
That's not what they're saying.
"Very many spam emails come from people running an email server on a dynamic IP. Some companies were happy to host spam sending companies, and would put them in dynamic ranges so they could continue to get money from those spam sending companies and keep changing the IP address. The ratio of good email servers to bad email servers on dynamic IPs is so poor that blocking all dynamic IPs is, unfortunately, the only reasonably solution".
You can be on a dynamic IP and send email. Just don't send that email from a server on a dynamic IP.