Block or unblock Port 25

Port 25 is part of an internet address that, as a rule, Spark blocks. Sometimes spammers use Port 25 to send viruses and spam. Spark filters Port 25 to stop the use of the Spark network, and our customers' emails, to send spam. Depending on how you send and receive emails, you may or may not be able to block Port 25. 

Blocking or unblocking Port 25

• To block or unblock Port 25, fill out the Port 25 block and unblock request form. View form
• Blocking or unblocking Port 25 can take up to two working days.
• When the changes are complete, restart your modem.

Who should keep Port 25 unblocked?

• If you host your own email service, you'll need to unblock Port 25.
• You don't need to unblock Port 25 if you use:
  • Xtra Mail, POP email (eg, Gmail).
  • A hosted service (eg, Spark Business Mail or Office 365).

Do other internet providers filter Port 25?

• It's best practice for internet providers to filter Port 25. It helps prevent the spread of spam and viruses.

Does Port 25 filtering only work with a static IP?

• You'll get an IP address when you sign up with your internet provider. A static IP doesn't change, while a dynamic IP can change.
• Port 25 filtering applies to static and dynamic IP addresses on ADSL, VDSL and Fibre.
• If you are on Wireless Broadband you need to have a static IP address to unblock Port 25.

When do I need to unblock Port 25?

• Check with your email provider to see if they have a secure port you can connect to.
• If your mail server doesn't support a secure connection on another port, unblock Port 25.
• If you host your own email, consider using a secure connection over a different port.

Will I still be able to send and receive emails using web-based email apps (eg, gmail.com and outlook.com)?

• Yes. To get your emails through these providers, you use your web browser. Your web browser uses a different port to your email app.

How does Port 25 filtering work on the Spark network when sending emails?

• Before letting emails through, it checks the source and destination internet addresses. It also checks the destination port, before letting emails through.
• If you use send.xtra.co.nz as your outgoing server, you won't be connecting by Port 25. You'll be using the secure Port 465, so filtering won't occur.

Related articles:

• The Port 25 block and unblock request form