Emails not delivered to Office 365 accounts

Article #:

Product

Castle

KB-139

Email

All

Summary

Customers using the Smoothwall's email relay may discover that emails are not being delivered to Office 365 accounts, even though they may be received by people with email addresses not using Office 365.

Problem

Customers using the Smoothwall's email relay may discover that emails are not being delivered to Office 365 accounts, even though they may be received by people with email addresses not using Office 365.

This is usually because of a feature of Office 365 (as well as many other email systems) called SPF - The "Sender Protection Framework".

Solution

The SPF system has a special set of instructions (called an SPF record) added to the domain name (DNS) entry for a given domain and details those machines, domains and IP addresses which are allowed to send email for that domain.

Microsoft, when using Office 365 advise that the SPF record for a domain should follow a format such as:

v=spf1 include:spf.protection.outlook.com include:spf.exclaimer.net ~all

You can read more about this in the Microsoft technical article available here. As the Smoothwall’s hostname or IP address is not listed in this record, the emails sent by the Smoothwall fail to deliver.

In order to resolve this issue, follow these steps:

On the Smoothwall, in the Reports > Settings > Output Settings section the SMTP Server should be set to 127.0.0.1

The sender's email address should be a real email address which can receive emails and is from the same domain used for Office 365

Amending SPF records for Office 365:

The externally hosted DNS record for the domain (such as example.com) should be amended to include an entry which includes the External IP address(es) of the Smoothwall. The Microsoft article linked in this document contains instructions on how to do so.

This configuration will not only allow the Smoothwall to send emails, but will instruct Office 365 (and any other systems which check the SPF record) to verify that the external IP addresses are allowed to send emails on behalf of that domain.

Attribution:

Last updated:

Author:

Contributions by:

21 June 2017

Tanja Ehrhardt

Darren Taylor

 

 


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