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 smtp.tds.net 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 (smtp.tds.net). Port 25 filtering will cause anyone attempting to send email directly from their computer or through a server other than smtp.tds.net to no longer be able to send email. They will need to change their outgoing email server to smtp.tds.net. 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 smtp.tds.net.  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 unauthorized 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 owned by TDS are sending mail. It will reduce the amount of spam being sent by TDS users as well as virus-generated emails.

The following is the default list of ports blocked by TDS:

 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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