Networking > Port Restrictions
Do you have any port restrictions?

We filter several ports that are known to be commonly exploited for various forms of malware. These ports, organized by protocol, are as follows:


  • 25 - Simple Mail Transfer Protocol (SMTP)
  • 139 - NetBIOS Session Service (NetBIOS-SSN)
  • 445 - Microsoft Common Internet File System (CIFS)


  • 135 - Microsoft Remote Procedure Call (Microsoft RPC)
  • 137 - NetBIOS Name Service (NetBIOS-NS)
  • 138 - NetBIOS Datagram Service (NetBIOS-DS)
  • 161 - Simple Network Management Protocol (SNMP)
  • 162 - Simple Network Management Protocol Trap (SNMPTRAP)
  • 520 - Routing Information Protocol (RIP)
  • 1900 - Universal Plug-and-Play (uPNP)
If you have issues connecting to email services served over port 25, it is generally recommended to instead connect over the more widely accepted TCP port 587. Port 25 is now reserved for mail relays only and is blocked by most internet service providers.

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