Third Party SMTP Blocking

From Lunarpages Web Hosting Wiki

Q: I am getting errors when I try to use my domain to send emails using my email client, but I can send just fine with my ISP SMTP settings. What is wrong?

A: Over the last few years, more and more ISP's have started to require their subscribers to use their SMTP server to send mail. This allows them to monitor spammers, and help to reduce to the overwhelming amounts of spam and exploitation that occurs daily with email. You may want to contact your ISP to see if they are willing to work with you on this issue or try port 587 or 26 which may be open on our servers. We can open an alternate port (587 or 26) on the server if necessary if you email

If you can not send email using our servers, check on this list below for your ISP or perform the test listed below. Provided with each ISP that blocks, is their respective SMTP server setting.

This list has been compiled by the Support staff over the last year. It is not an official release of ISPs that require that there clients use their SMTP servers, however, it is as accurate as possible at this time.

Testing SMTP server access:

  1. Access a command line (in Windows, Click Start -> Run, and then type in CMD; on a MAC, use the Terminal application in the Applications/Utilities folder.)
  2. Type in TELNET DOMAIN.COM 25 (replace DOMAIN.COM with your actual domain name)

If you are not being blocked from your ISP, you should see the following message: ESMTP Exim 4.34 #1 Fri, 02 Jul 2010 13:20:48 -0700
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.

If you do not see this error message, your ISP is very likely blocking the ability to send mail through servers other than theirs.

ISP's that Block Port 25

  • AOL:
  • Adelphia:
  • Ameritech:
  • Astound Broadband:
  • AT&T:
  • AT&T Global:
  • Bell internet highspeed (Canadian):
  • Bell south:
  • (Australian): contact service provider for Settings.
  • Bresnan Communications:
  • BT Yahoo in the UK: contact service provider for Settings.
  • CableOne:
  • Charter Communications:
  • Cinncinnati Bell/Fuse Dial-up:
  • /east / central
  • comcast:
  • Cox: - -
  • Earthlink:
  • Embarq : contact service provider for Settings:
  • epix:
  • erols:
  • Etisalat (UAE):
  • fuse:
  • Juno:
  • Megared (Mexico): contact service provider for Settings.
  • Mindspring:
  • MSN:
  • MSN.DSL:
  • Netcom:
  • NetZero:
  • OOL (Optimum Online):
  • Optusnet:
  • Pacific Bell (Pacbell):
  • PeoplePC:
  • Plala:
  • Puget Sound Network, Inc. : contact service provider for Settings:
  • RCN:
  • Road Runner(NYC): (for other states, and regions contact your Road Runner Support team)
  • Rogers Hi-Speed (Canadian):
  • SBC:
  • SBC Yahoo:
  • shawmail
  • Speakeasy:
  • Suddenlink:
  • Sympatico:
  • Tedata:
  • Telus: check with ISP
  • Verio:
  • Verizon: (please note that Verizon FIOS should not have any issues with SMTP blocking, only the DSL or other services)
  • Verizon(alt): (please note that Verizon FIOS should likely not have any issues with SMTP blocking, only the DSL or other services)
  • Videotron:
  • (Canadian): contact service provider for Settings.

More will be added as we go, but this is as comprehensive a list we have to date.

If you know of another ISP and it is not listed here, please let us know and we'll be sure to add it.