Port 25 (SMTP) Blocking ISPs
Many dial-up providers are now blocking port 25 (SMTP/Outgoing Mail Gateway) access
from their clients to all servers other than the ISPs mail servers.
This means that hosting clients which have ISP service from these providers will not
be able to use the SMTP service provided with the hosting accounts (this includes all
hosting providers) and must use the mail server of their ISP.
Known ISPs who block remote Port 25/SMTP Access
| ISP | Outgoing Mail Server |
| AltaVista Free Access | email.1stup.com |
| AT&T WorldNet | mailhost.worldnet.att.net |
| Cox.net | smtp.west.cox.net |
| DCAnet | postoffice.dca.net |
| EarthLink | mail.earthlink.net |
| Microsoft's MSN | smtp.email.msn.com |
| MindSpring | smtp.mindspring.com |
| NetZero | smtp.netzero.net |
| Prodigy Internet | smtp.prodigy.net |
| SBC Global (Yahoo) | smtp.sbcglobal.net or smtp.sbcglobal.yahoo.com |
| Sprynet | smtp.sprynet.com |
| Verizon/GTE (Dial-Up) | smtp.verizon.net |
| 
