TDS Internet Support

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TDS Blocking of Internet Ports

TDS blocks several ports including port 25.

Who is affected by Port 25 (SMTP) filtering?

Most TDS customers will not be affected by Port 25 filtering and will not need to change any email settings. However, all dynamic TDS Internet customers who are connected to TDS but not currently using as their outgoing email server will be affected by this change.


What is affected?

If a TDS customer wishes to send email while connected to TDS, they need to use the TDS outgoing mail server ( Port 25 filtering will cause anyone attempting to send email directly from their computer or through a server other than to no longer be able to send email. They will need to change their outgoing email server to If you are having problems and wish to check the settings in your email client (e.g., Outlook Express), search our FAQs for instructions for changing your email settings. Port 25 blocking affects outgoing mail only, not incoming.
(Note: If you are not connected through a TDS connection you will not be able to use  You will have to use the SMTP server of the ISP you are connected through.)


When did this start?

TDS started filtering port 25 in April 2004.


Why is TDS Filtering port 25?

TDS has been forced to filter SMTP port 25 in an attempt to cut down on the amount of spam being sent from the TDS Network. Filtering port 25 will prevent spammers and computers with viruses from sending unauthroized spam/virus messages. This means TDS will be able to provide you even better email service with less chance that your legitimate email will be blocked by other ISPs!


How port 25 is used:

Port 25 is the port an email application uses to send mail to the email server for delivery. Filtering this port ensures only legitimate email servers found by TDS are sending mail. It will reduce the amount of spam being sent by TDS users as well as virus-generated emails.

Protocol Port
tcp 135
udp 135
udp 137
tcp 139
udp 139
tcp 445
tcp 593
tcp 707
tcp 4444
udp 995
udp 996
udp 997
udp 998
udp 999
tcp 1433
udp 1433
upd 8998

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