Comcast is now blocking smtp on port 25 – Use port 587 instead


If you try to send email using comcast smtp server on port 25 your outgoing email will be blocked. Choose instead port 587 and the problem goes away. See below Comcast explanation:

“Port 25 is an unsecured port on a computer that those sending spam can take control of to send spam – often without the user ever knowing his/her computer has been compromised. When spam from a compromised computer is detected, Comcast’s anti-spam systems automatically apply a sending block and send an email notification to the affected subscriber’s comcast.net email address. This block does not interrupt mail service for Webmail (e.g. Comcast, Yahoo, Gmail, or Hotmail); however, this block does prevent email programs or clients (e.g. Outlook Express) from sending email. Client e-mail programs will still receive email. The instructions at our mail client help page explain how to configure common email client programs to use Port 587, which includes authentication, instead of Port 25.”

Other ports blocked by Comcast:

Port# Transport Protocol Direction
68 UDP bootp/dhcp Inbound
135-139 TCP/UDP Netbios Both
445 TCP MS-DS-SMB Both
520 TCP/UDP RIP Both
1080 TCP SOCKS Inbound

Explanation for port 68:

UDP Port 68 is used by customer computers to obtain dynamic Internet Protocol (IP) address information from the Comcast’s dynamic host configuration protocol (DHCP) server that assigns IP addresses to customer computers. DHCP ports can be used for malicious attacks such as, for example, obtaining access to a customer’s home computer or home network and its devices

Explanation for port 135-139

NetBios services allow file sharing over networks. When improperly configured, they can expose critical system files or give full file system access (run, delete, copy) to any malicious intruder connected to the network.

Explanation for port 445:

Security risks; vulnerable to attacks/exploits/worms such as the Sasser and Nimda worms..

Explanation for port 520:
Vulnerable to malicious route updates which provides several attack possibilities.

Explanation for Port 1080:

Multiple vulnerabilities (Viruses, Worms, DoS attacks).

Source: comcast secure chat web site (web link doesn’t work because it is a secure link)

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