Upgrade for Live Support

All of our paid plans come with access to our highly experienced technical support team.

  • Contact us via Email, Phone, or Ticket
  • Detailed Explanation of Your Lookup Results
  • Guidance to Help Resolve Your Problems
  • RFC Compliance Best Practices
  • Blacklist Delisting Support

Let our experts help you resolve your smtp issue!

Get Smtp Support

SMTP Connect

What you see when your domain has this problem
Unable to Connect to SMTP Host Details area Ignore

More Information About Smtp Connect

We attempted a connection to your mail server on port 25 but your server did not respond. More than likely there is no email server at this address or you have a misconfigured firewall or spam filtering system.

If the SMTP Connect test is unable to connect to your mail server after 15 seconds we will report it as an error. For optimal email deliverability it is advisable that SMTP connections should not take longer than 15 seconds.

Firewall Information

Here are the networks MxToolbox uses for SMTP Tests. Please add these to your firewall to avoid experiencing connection failures or false alerts.

  • 64.20.227.128/28 (Netmask: 255.255.255.240)
  • 208.123.79.32/27 (Netmask: 255.255.255.224)
  • 54.84.234.24, 54.164.124.219, & 54.88.4.135

Additional Information

Tarpitting

It is also possible your server is “Tar pitting.” Tar pitting is a technique used by some email servers to slow down spammers. The idea is that legitimate senders will wait longer to establish a connection than spammers will.

Here is a link to a link to the TechNet article with more information about Tarpitting

Back Pressure

Our SMTP test cannot detect problems caused by Back Pressure, a system resource monitoring feature of the Microsoft Exchange Transport service. In order to be alerted for back pressure events you would need to add our end-to-end Mailflow Monitor for your server which can detect any type of email interruption and also provide historical performance data.

Here's a link to the TechNet article with more information about back pressure.

Are you confident your email is getting through?

You rely on email for business critical communication, so you need to know your email has been delivered to your customers and you need to know who is sending email on your behalf.

MxToolbox is YOUR expert on email deliverability. Delivery Center analyzes your DMARC, DKIM and SPF to give you the insight you need to make email configuration changes and get your emails to your customer's inboxes.
Learn More

 
burritos@banana-pancakes.com braunstrowman@banana-pancakes.com finnbalor@banana-pancakes.com ricflair@banana-pancakes.com randysavage@banana-pancakes.com