SMTP Relay Errors

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What is SMTP Relaying?
What are the symptoms of a relaying error?
How do I whitelist the IPs?

What is SMTP Relaying?

SMTP Relaying lets you send email messages composed in through your email account using your mail server's existing SMTP service. This allows you to use to compose and send email messages, but the actual email messages are processed through your mail server's SMTP services. does not require a fully open mail relay, but does require that the server IPs are allowed to relay email in your environment.

The list of server IPs is listed here.

What are the symptoms of a relaying error?

The symptoms of a potential relaying error are:
  • Emails being bounced back or unable to be sent.
  • Emails being stuck in the Outbox.
  • Customers not receiving their emails
  • Similar error message to the ones below appearing in your error logs:
              → 550 5.7.1 Unable to relay\r\n
              → 550 5.7.1 Unable to relay for customer@theircompany.comr\n
              → 554 5.7.1 <>: Relay access denied\r\n
              → 511 Host Not Authorized to Relay\r\n
              → 550 relay not permitted\r\n
              → 553 5.3.0  Rejected or Address Rejected
              → 553 5.3.0  Address Rejected
              →​Unknown or illegal alias
              →​No such user here
              →​server does not allow relaying
              →​553 Relaying disallowed

These errors are the mail server's way of telling that it is not configured to allow it's IPs to send emails.

How do I whitelist the IPs?

Since there are many different mail server brands and network environments with their own method and requirements for whitelisting, you would need to contact your email server administrator(or email service provider) or network administrator to allow the IPs. It is critical that the whitelist is implemented properly.

In most environments, whitelisting on the mail server alone is sufficient. However, if you are using any of the following  security applications or devices, additional whitelist configuration or exceptions may be required:
  • Spam Filter
  • Antivirus
  • Endpoint application
  • Firewall
  • Router
  • Front End Relay Server
Please consult with your email server administrator or network administrators regarding the whitelist.

If you use a hosted spam filtering service, such as Microsoft Exchange Online Protection,  Microsoft Forefront Online Protection for Exchange or a similar service, you may need to contact your provider to discuss the errors and determine if any whitelisting needs to be done for the IP's.

Check your SPF records

You should also verify that your sites' SPF  records are configured properly. Please go to and enter your domain name without the www. ie: This should give you your SPF record. Make sure there are no restrictions on what sites/domains can send email in your company.

To test the IP addresses against the SPF record, you can use this SPF Policy Tester tool. 

Plug in one of the IP addresses from the list of allowed IP addresses from earlier in the article. Then plug in your sending email address in the second field. If the tool returns a failure, then the SPF record is incorrectly configured.

It's not always the case, (THIS IS NOT REQUIRED) but if your network administrators do require an SPF record for these IP addresses, we suggest using the SPF Wizard to rebuild your SPF record to include the IP addresses from the article above.

You should consult with your Network Administrators before attempting any SPF record changes in DNS, as doing this improperly can cause serious problems for your email system.

I have whitelisted the IPs and verified that my SPF record is not causing the issue, but am still receiving the relay error, now what?

If you feel that you have applied the whitelist correctly, and continue to receive a relaying error, then you may have missed a device or exception in one of your applications/devices. 

If you are still having issues, it is highly recommended that you get your email server administrator or network administrators to sniff out the whitelist IPs on your network and locate the failure point. The servers will try to send an email every minute or two, and the connection attempts should be easily visible in your network and mail server logs.

Proper whitelisting is required in order for to function properly when sending mail. While the support team can provide guidance on the potential failure points, the actual configuration is done entirely in your own or your hosting provider's network environment.