Port 25

Port 25 is the Dedicated Internet Port used for sending email. It is also used by spammers to send unwanted email, new viruses and worms will often spread across the Internet using this port. That's why we filter it.

Want to Block/Unblock Port 25?

Port 25 Unblock

In an average week, Spark Anti-Spam filter detects, marks up or removes over 40 million pieces of spam email. That's a very good start however some spam still gets through. To help tackle this problem, we filter email traffic on the email Port 25.

What is Port 25 unblocking and what customers will be unsuitable due to this limitation?

Customers who run their own email service will need Port 25 to be unblocked. Customers who use Xtra email or POP email (e.g. gmail) or a hosted email service (e.g. Spark business mail, Office 365) are not affected by this limitation.

  • Port 25 is typically used by customers who send mail from their own email server
  • Spark (Xtra) routinely block Port 25 in line with best international practice as a control against spamming

Do other Internet providers filter Port 25?

Filtering Port 25 traffic is now regarded as international best practice to help prevent the spread of spam, worms and viruses. Many large ISP's in Europe, USA and Australia have now adopted this practice.

Does Port 25 filtering only work with a Static IP?

No, Port 25 filtering applies to the IP addresses assigned to the username regardless of whether it is static or dynamic. If the username has Port 25 opted out then the IP address assigned to this username will have Port 25 filtering turned off.

When do I need Port 25 filtering turned off?

If you are running your own mail server on a Spark - assigned IP address, or, you are using Third Party server settings then you will need to be opted out of Port 25 filtering.

Will it prevent me from sending or receiving emails using web based email providers such as yahoo.com and hotmail.com?

No it will not. Online email such as Yahoo and Hotmail are all web based services and allow you to use your web browser to access them. Your web browser uses a different Port from your dedicated email program.

How does Port 25 filtering work on the Spark network when it comes to sending email?

Port 25 filtering is a type of rule that checks the source IP address, destination IP address and destination Port before allowing the traffic. So it leaves only destination IP address to be checked. If you are using smtp.xtra.co.nz as your outgoing server, the destination IP address will be the IP address of that server (email is being sent to that server from the computer first) so filtering does not take place. But if you are using different server addresses, Port 25 is filtered.

Blocking or Unblocking

It can take up to two working days to opt in or out of Port 25 on a working broadband line. After successfully opting out, you will need to restart your broadband modem.

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