We get calls from customers all around Australia needing help with their email. Since the start of October 2022, we started to see a spike in Optus customers that could receive emails but couldn’t send them. We’d seen this problem many times before and it was always a misconfiguration problem on the customers email client. This new spate of problems showed us that the customers email client was configured correctly, and that the problem disappears when their computer is in our shop.

If this sounds like a problem you are currently experiencing, read on to find out why it’s happening and how to fix it.

Why can’t Optus customers send emails?

We’ve found that Optus is blocking port 25 on mail.optusnet.com.au for connections coming from some (not all) Optus connections. We first saw this problem back in early October and would have approximately 1 customer per week call with this issue. The number of affected customers has continued to grow and yesterday, we had 4 customers call with this exact problem.

What does port 25 do?

Port 25 is the port Optus advises customers to use to send emails via their mail.optusnet.com.au SMTP service. A successful connection to port 25 on mail.optusnet.com.au is essential before an email can be sent, and this connection takes place before your email address and password is presented for authentication.

Steps to confirm Optus are blocking port 25

Firstly, lets confirm you are definitely within scope.

  • You are an Optus customer with an optusnet.com.au email address
  • Your home NBN and/or 4G service is with Optus
  • You can receive emails to your optusnet.com.au email address but cant send from your optusnet.com.au email address
  • You have signed into your Optus webmail and can send emails successfully from there
  • You can use your computer to send emails from your optusnet.com.au email address when you connect to a different network or hotspot to a 4G service on a different service provider (ie Telstra).

If you’ve answered yes to these questions, you are within scope and should run the below check for your computer to see whether you are directly affected. If you couldn’t confirm the last question, lets assume that’s a yes too and move on.

Windows 8, 8.1, 10, 11 Users

1. Open a PowerShell session. If you’re not sure how to, click the Windows start button on your Taskbar and type PowerShell, then press .

2. Run the following command in your PowerShell session
tnc mail.optusnet.com.au -port 25

Powershell screen grab showing a failed connectivity test of port 25 on mail.optusnet.com.au

Here’s what a failed connection type looks like. The yellow warning line tells us that this computer couldn’t connect to the Optus mailserver on port 25 because the connection was refused, and thats a problem only Optus can fix.

If theres no yellow warning line and your TcpTestSucceeded line reads true, you are not affected by this Optus issue. If your email still isn’t working, your problem lies else where. See the bottom of this post for more tips.

Windows 7 Users

Follow this Microsoft article to enable telnet.

Once telnet is installed, open a command prompt. You can do this by In Windows 7 by holding down the [windows] button on your keyboard and pressing the key, typing cmd in the Run box and hitting [return].

When the command prompt box appears, type in the following line and press [return].
telnet mail.optusnet.com.au 25

Screen grab of command prompt window showing failed telnet connection

Here’s what a failed connection type looks like. This tells us that your computer couldn’t connect to the Optus mail server on port 25 because the connection failed, and thats a problem only Optus can fix.
Connecting To mail.optusnet.com.au...Could not open connection to the host, on port 25: Connect failed

Conversely, a successful test will return the below result:
220 mail104.syd.optusnet.com.au ESMTP Postfix
If you get this result, you are not affected by this Optus issue. If your email still isn’t working, your problem lies else where. See the bottom of this post for more tips.

Apple MacOS and OSX users

Open terminal on your Apple computer by holding down [command] and pressing [space] to bring up the spotlight search bar, then type terminal and select it from the results.

MacOS spotlight window showing results when searching for terminal

Once you’ve opened terminal, type in the following command and press [return]

curl -v telnet://mail.optusnet.com.au:25

MacOS terminal window showing a failed connection test
Here’s what a failed connection type looks like. This shows us that our computer could not establish a connection to the Optus mail server on port 25. This is a problem Optus needs to fix.

If you see a “* Connected to mail.optusnet.com.au ( port 25 (#0)” prompt, your connection has been successful and you are not affected by this Optus issue. If your email still isn’t working, your problem lies else where. See the bottom of this post for more tips.

If you got a failed connection test, read on.
If your connection was successful, your problem lies elsewhere.

I got a failed connectivity test – what does this mean?

The command you just ran attempts to connect to the Optus mail server on port 25, the port that Optus have designated for sending emails. If your computer cannot connect to port 25, no email client (ie Outlook, Thunderbird, Windows Mail, Windows Live Mail) that runs on your computer will be able to send emails. This is why its not necessary to check your email address or password to confirm this test because this issue occurs before Optus has had a chance to ask for your authentication details.

If you are a residential customer, this is all the proof you need to take to Optus to show them there is problem on their side.

Why can I send emails from the Optus webmail site?

When you call Optus, their troubleshooting often involves guiding customers to the Optus webmail site and having the customer send a test email from there. When the email succeeds, Optus will make the claim “well this proves theres no issue sending emails on our side, so the problem must be on your side, try checking your Outlook settings” etc.

Using webmail successfully confirms that you have the right password, the right email address and that your account is active with Optus, but it does not confirm that sending emails via SMTP from your home should be ok. Webmail does not initiate an SMTP connection from your home – it initiates an SMTP connection from the Optus webmail server.

Why is Optus blocking port 25 for their customers?

It’s likely Optus are trying to fix one problem and have created another in the process.

That being said, the use of port 25 is legacy, and it is unorthodox to use port 25 for encrypted TLS connections (465 and 587 are often used, however the IETF encourage the use of 465). Perhaps Optus are looking to move everyone to STARTTLS on 465 and blocked port 25 too early?

I’d already spoken to Optus and they told me (incorrectly) that my computer is the problem. Why cant they identify the problem?

The Optus call operators follow a script. Their current scripts don’t include testing port 25 on customers computers and the call operators typically don’t have a background in email support.

How do I get Optus to fix my email?

Call Optus Support on ph. 13 39 37 and tell them this:

“I haven’t been able to send emails from my optusnet.com.au email address for the past week. I have performed a port connectivity test from my home computer and have found that when I connect to port 25 on mail.optusnet.com.au, my connection is refused. Can you please remove the block on port 25 so I can send emails through the Optus email server.”.

If you haven’t already verified your identity, the call centre operator may ask more questions to confirm who they are speaking to. You’ll need to answer these questions.

Once they have pulled up your account details, they may want to have you perform tests. Just say “no thank you, I just need port 25 unblocked so I can send emails”.
When the operators confirms that the port has been unblocked, run the command above again and you should get a successful connection.
At this point, you can thank the call operator for their assistance and end the call.

Do I need a static IP address to fix this problem?

Today, a customer of ours shared this blurb they received from Optus:

“It’s an issue where Microsoft has blocked Optus IP addresses. That means, those using Outlook with an Optusnet email will be impacted. Using a Static IP, our team has determined will work as Microsoft has not blocked those IPs. As mentioned, it is an issue with Microsoft blocking IPs, not Optus. Nevertheless, our team is working on this to see what can be done with Microsoft to revert blocked IPs. However, as this is an issue on Microsoft’s end for blocking the IPs, there’s not much more we can do. I’d suggest using an alternate option, as mentioned in the meantime, if you don’t wish to activate a Static IP.”

It’s not clear to us why Optus have started blaming Microsoft. Optus manage their own mail server, and Optus manage their own firewall rules. Many Optus customers don’t use Outlook. This explanation does not make sense.

A static IP address may fix the problem, but Optus customers shouldn’t need to purchase an upgrade to fix a problem that Optus have caused when a simpler (free) solution is to just remove the block on port 25.

If Optus offer a static IP address to fix this problem, you should ask them to escalate your case to someone that has authority to speak with the network team. Once you reach that person, ask them to have port 25 unblocked and tell them you aren’t interested in paying for Static IP address.

We know this escalation approach currently works, however Optus seem to be regularly changing their tact on solving this problem.

Still cant send emails?

One side effect from this problem is users have been using google/facebook to find solutions, and then changing their previously working email configuration in a hope to fix the issue themselves. Unfortunately, the configuration was fine to begin with and instead of fixing the problem, they inadvertedly broke their email configuration.

To configure your email client to send emails via the Optus mail server, you need to use the following settings:

SMTP Server mail.optusnet.com.au
Username Your Optus email address
Password Your Optus email password

This is too difficult, can you fix this for me?

We get it, technology is confusing. Give us a call on 02-8502-8954 Monday to Friday 9am to 5pm, and we can book you in for a remote session. We charge $165 an hour in 15 minute increments. Most calls take 15-30 minutes.

Fed up with Optus?

Give us a call on 02-8502-8954 Monday to Friday 9am to 5pm and we can book you in with a technician for a consultation. We can then explain whats necessary to leave Optus, and help you with the move.

Many customers have also taken to raising cases to the Telecommunications Ombudsman.

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