Learn how to troubleshoot email not sending on O2 Mobile Broadband by changing your SMTP settings from port 25 to port 26.


Email does not send if you send an email using O2 Mobile Broadband.

Your email application on your iPhone, Outlook, Mail, Thunderbird, or iPhone or other email client may timeout when sending or return the following error;

SMTP 554 Transact Failed – Transaction failed; Port 25 error; The connection to the server has failed- Error Number: 0x800CCC0E


O2 Mobile Broadband restricts access to SMTP email on port 25.


If you’ve upgraded to DomainsFoundry Roaming SMTP or subscribe to DomainsFoundry SMTP for iPhone, you can configure your email application to access your SMTP server on port 26. See How to change SMTP port number.

Changing to port 26 tells your email application to connect to our SMTP servers using a different route and bypasses 02’s restrictions.

If you use your ISP to send email then you’ll need to contact your ISP for assistance. Changing the ports may still work, but you’re best asking them first if they support SMTP over port 26.

Using port 26 but still can’t send?

If you’ve updated to port 26 or are already using port 26 and still can’t send email, please consider the following;

  • Double-check your SMTP settings.
  • Some mail apps require restarting for changes to come into affect.
  • Check your firewall is allowing access over port 26.
  • Many ISP’s limit access to their SMTP to ensure you only use it for home use. If you’re trying to use your ISP’s SMTP service and ask your ISP is they support SMTP over port 26.

My ISP only supports SMTP on port 25. What now?

Why not consider our Roaming SMTP service. DomainsFoundry Roaming SMTP gives you a flexible, dependable and simple SMTP service that you can rely on. Use at home, work or on the move. For a low monthly fee, you can send email from any location, computer or phone – including iPhone. See [[How can I order Roaming SMTP?]]

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