Email trigger initiation issues ("Relay access denied")

Have you set up an email trigger, and you're sure you've followed all the instructions but when you send the email to the right address...nothing happens? Or maybe you see a bounce indicating the message was rejected due to something called a "Relay access denied" error?

The issue

The issue is that your SMTP server is configured to allow CNAME expansion for email addresses. With this feature enabled, the email server can sometimes change the "to" address for emails when routing them to their destination.

To use email to trigger a flow in xMatters, you must send an email to an address matching the following format:
<recipient>@<triggerID>.<company>.xmatters.com

But with the CNAME expansion option enabled, an email sent to 
mmcbride@traveladvisory.example.xmatters.com 
might be changed during transit through your email server to something more like
mmcbride@us1-west-1.mail_traveladvisory.example.xmatters.com.

The solution

To resolve this issue, you need to work with your IT team to disable the CNAME expansion setting on your SMTP email server.

As an example, here's a description of the CNAME expansion setting on a Sendmail email server (from the Sendmail documentation):

confDONT_EXPAND_CNAMES	DontExpandCnames
					[False] If set, $[ ... $] lookups that
					do DNS based lookups do not expand
					CNAME records.  This currently violates
					the published standards, but the IETF
					seems to be moving toward legalizing
					this.  For example, if "FTP.Foo.ORG"
					is a CNAME for "Cruft.Foo.ORG", then
					with this option set a lookup of
					"FTP" will return "FTP.Foo.ORG"; if
					clear it returns "Cruft.FOO.ORG".  N.B.
					you may not see any effect until your
					downstream neighbors stop doing CNAME
					lookups as well.

More information

xMatters does not use CNAMEs for their mail servers. Instead, mx records go to load balancers, and the request uses the load balancer address instead of the instance hostname which is required to properly source the initiation.

For a more thorough explanation of CNAME expansion, check out these SMTP articles from IETF.org:

• RFC 2821
• RFC 5321

(To save you a little time, the money quote appears to be this one: The lookup first attempts to locate an MX record associated with the name. If a CNAME record is found instead, the resulting name is processed as if it were the initial name.)

For more information on using email to integrate with xMatters, see the email trigger description in the online help.