Issues Sending Email and ISP Blocking
If you are having problem sending emails, make sure you are certain you have followed the instructions for setting up your email client to sendmail, including checking the "my server requires authentication" check box. The other possibility could be your ISP.
Most ISP's block sendmailís default port of 25.
To correct this problem simply, configure your SMTP settings to use your ISP's SMTP settings.
The following links are websites that has a list of known ISP that block the use of third-party smtp servers.
Earthlink Internet service: smtp.earthlink.net
MSN Internet service: smtp.email.msn.com
Verizon Internet service: outgoing.verizon.net
Qwest Internet service: pop.dnvr.qwest.net
OPTOnline Internet service: mail.optonline.net
SBC Internet service: smtp.sbcglobal.yahoo.com
SCB (Pacbell): mail.pacbell.net
SCB (SBC Global): smtp.sbcglobal.net
Comcast Internet service: smtp.comcast.net
At&T Broadband Internet service: mail.attbi.com
Cable One: mail.cableone.net
XO Communication: mail.njd.xo.com
Cox Internet: Find your SMTP server based on your State:
Cox Internet State-specific SMTP server names.