Blocked & MSLN specific ports

This guide lists the ports currently blocked on the borders of the MSLN network, as well as the ports MSLN services designate for specific applications.


  1. Blocked Ports
  2. MSLN Port Designations

Blocked Ports

All of the following ports are blocked on the borders of the network due to abuse by bad actors and prolific viruses:

  • TCP/UDP 135-139 (Windows NBT)
  • TCP/UDP 161-162 (SNMP) - Blocked throughout the network for non MSLN-owned equipment.
  • TCP/UDP 445 (Windows SMB)
  • TCP 1433 (MS SQL Server)
  • UDP 1900 (Universal Plug and Play)
  • UDP 19 (CHARGEN)
  • UDP 111 (PORTMAP)
  • UDP 137-138 (NETBIOS over IP
  • UDP 520 (RIP)

In addition to these ports, the following lesser used or known-vulnerable IP Protocols are blocked:

  • Protocol 53 (SWIPE)
  • Protocol 55 (MOBILE)
  • Protocol 77 (SUN-ND)
  • Protocol 103 (PIM)

Finally, we block outgoing traffic on port 25 to all destinations except our own SMTP server. If you wish to use port 25 for sending mail, please specify as your SMTP server.

See more information at the MSLN Email FAQ.

MSLN Port Designations


Our mail server accepts incoming SSL connections on 3 ports:

  • 25
  • 465
  • 587

Some ISP's do not allow outbound port 25 traffic. Verizon and are two ISPs that do not allow outbound port 25. In order to get around this, use one of the other two ports listed above. See our Email Client Configuration Guides for instructions.

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