[jlgaddis]

"Many ISP's" don't actually block 25/TCP outbound but simply add their residential netblocks to, e.g., the Spamhaus PBL. An end-user assigned one of these IPs can, upon request, have it removed from the PBL himself. This is, IMO, a much better way of "disallowing" outbound SMTP than simply filtering out packets.

[c22]

I'm curious as to why this is better in your opinion. Doesn't adding the range to a blocklist carry the potential of being copied by other blocklists? Then an ip seeking to send mail must track down and request removal from every blocklist that it's been added to whereas the alternate approach requires the email administrator only contact a single entity, and one they are a customer of to boot.

[jlgaddis]

If, as an end user, your IP address is on the Spamhaus PBL, you can have it removed yourself simply by submitting a request online.

If packet filters are used to block 25/TCP, you have to request that your ISP unblocks it, hope that they do, and then wait for them to actually do it.