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SMTP block for dynamic DSL users
Last updated: December 21 2009
What is "port 25" and SMTP?
TCP port 25 is the communication channel used to send most e-mail on the Internet. The protcol for sending mail is SMTP (Simple Mail Transfer Protocol). The SMTP protocol is used both by mail clients communicating with mail servers and among mail servers communicating with each other. However, port 25 is used typically for communication between e-mail servers only and not e-mail clients (other ports are used for client-to-server communication).

What has Caneris changed?
On December 20th 2009, Caneris implemented port 25 blocking for dynamic DSL users. These are most of our DSL users, who do not have a static IP.

Why was this done?
This was done to curb spam being sent from our network, mostly by infected customer PCs. The number of abuse complaints we have received and the number of our IP addresses blacklisted over the past several months have neccessitated these changes. Our block applies to dynamic IP addresses only, where the majority of e-mail sending PCs on port 25 are Windows machines infected with a virus or other malware and whose owners have not taken appropriate precautions to prevent this. Customers using static IP addresses are not affected by this change.

How does this impact me?
Most customers are unaffected by this change and do not need to take any action. If you are using our mail service to send mail, you are unaffected. If you are using any type of e-mail service which uses a web-based interface (through your web browser), you are unaffected. If you are using a third party service, you are likely unaffected. If you are unable send mail, please see below.

I am unable to send mail after the change.
If you have a static IP or opted-out and are still unable to send mail, please contact support via the customer portal. Otherwise, you will need to use ONE of the solutions below, in order of preference:
  1. If you are using a third party e-mail service or otherwise send mail via port 25 to a server outside our network, please contact your e-mail provider to request an alternate port, such as 587, the mail submission port. In nearly all cases, you will be able to resolve this issue by doing this simple change.
  2. Consider using our outbound SMTP server. Settings:
    • Server name:
    • Port: 587
    • Encryption: TLS
    • Authentication: required - use your PPPoE login
    • This server is accessible from outside our network as well - no change in settings is required
    Instructions/screenshots for Outlook 2003
    Instructions/screenshots for Outlook Express 6
    Outlook 2000 is nearly identical to Outlook Express 6
  3. If you operate your own MTA or otherwise require port 25 outbound access from your DSL connection, you have the following two options (choose only one):
    1. (Recommended) Obtain a static IP address from us ($4/month). Static IP addresses are not subject to this block.
    2. Submit a dynamic IP SMTP block opt-out request by contacting support via the customer portal
    It is your responsibility to keep your computers and home/office network secure. If you opt-out and spam is detected, the port 25 block will be re-instated for your account.

I have an infected Windows PC. How do I clean it?
You can try our MalwareBytes package (self-installer). Be sure to update it after installing. We also recommend you obtain an anti-virus.

You claim you do "no blocking", but now you are blocking something
The port 25 block is on an "opt-out" basis and affects dynamic DSL customers only. Sending mail is not blocked. Users continue to be able to send mail using any of:
  • Our mail service
  • Third party service on ports other than 25
  • Webmail services
  • Port 25, using a static IP
  • Port 25, by opting-out and using a dynamic IP address as before
All Caneris services are subject to an Internet Acceptable Use Policy.