It's been extremely effective in blocking spam sent by spambots on large ISPs. It's not a magic anti-spam bullet. (If you know one, please let us know.)
That simply hasn't been my experience. I still get lots of spam from booted hosts in large provider networks, and yes, that includes many
It's extremely effective for us (not a large provider by any means). We block outbound 25 on all dynamic IP customers - to date it's never been a problem for our customers. Customer's who have static assignments are not blocked by default. Paul -----Original Message----- From: John R. Levine [mailto:johnl@iecc.com] Sent: Friday, September 03, 2010 3:20 PM To: Owen DeLong Cc: nanog@nanog.org Subject: Re: ISP port blocking practice that block 25. As near as I can tell, 25 blocking is not affecting spammers at all, just legitimate users. I know people at large ISPs with actual data. Port 25 blocking is quite effective. R's, John