Custom Bounce Domains

What is a bounce address?

A bounce address is another term for the return path address.  This is an email address specified during the SMTP protocol communication process that determines where the receiving mail server sends back its bounce and error messages.   

What is a Custom Bounce domain?

For the delivery of all messages through the SocketLabs platform our systems generate a Variable Encoded Return Path (VERP) address. When we generate this email address our system uses a SocketLabs owned domain `` by default. An example of a VERP address is:
A custom bounce domain allows you to customize the domain utilized in the these email messages.  The above example would look like the following when customized for

What is Required to Set-Up a Custom Bounce Domain?

In order to set up a custom bounce domain, a CNAME record must be established with your DNS service provider. This CNAME must point a subdomain to the domain. This can also be used for enabling the Engagement Tracking feature. You can re-use the CNAME record created for engagement tracking to customize your bounce domain. For more information please see our knowledgebase article on CNAME Configuration for Bounce Tracking. We now also support validating chained CNAME records for Custom Bounce Domain. For organizations providing services to sub-clients, you can have your client create a CNAME record to your own sub-domain, and create another CNAME record pointing that to SocketLabs.   An example of this would be:
bounces.client-example.tld CNAME bounces.your-domain.tld 

bounces.your-domain.tld CNAME 
Prior to permitting any Custom Bounce Domain entry to be added to your domain list we will verify the CNAME record properly exists in DNS.    

Multiple Custom Bounce Domains

You can add multiple custom bounce domain entries in the SocketLabs Control Panel. We will automatically select the appropriate bounce domain for each message processing through your server based on the address in the From headers of the email message. The domain in the From address field of a message must be a parent domain of a provided custom bounce entry. If no match is found, then the default Custom Bounce Domain entry will be utilized.   Example:
From: "SocketLabs" <no-reply@RECEIPTS.EXAMPLE.COM> 

Bounce domain: bounces.RECEIPTS.EXAMPLE.COM

Default Custom Bounce Domain

When a message is processing through your server and the domain portion of the address in the From field of the message headers does not have a organizational domain matching Custom Bounce Domain entry, then the default Custom Bounce Domain will be applied. If no default value is established, then the SocketLabs domain of  ""  will be utilized. Each server may only have a single default value configured.

Custom Bounce Domains and DKIM Signing

We highly recommend establishing a custom DKIM signature for your organizational domain while setting-up a Custom Bounce Domain. This will provide a completely white-labeled email delivery experience, and ensure the best deliverability for your messages. Most customer using our service for sending on behalf of a single domain would look similar to:
From Address:  sales@CUSTOMEREXAMPLE.COM 

Custom Bounce Address: <>

Custom DKIM signature domain: D=CUSTOMEREXAMPLE.COM
For more information about the SocketLabs platform and DKIM signatures see our articles on the topic: 

Why is a Custom Bounce Domain important?

Many customers have requested this feature in order to white-label the email messages sent via our platform. It removes traces of the SocketLabs service from the SMTP protocol communications.  Having a customized bounce domain is also important for an up and coming email technology called DMARC. DMARC, which stands for Domain-based Message Authentication, Reporting & Conformance, allows domains to protect themselves from being spoofed in email messages. The technology is built on top of existing email authentication technologies SPF and DKIM.  DMARC requires the bounce domain and from address domain to align. DMARC does permit the bounce domain to be a sub-domain of the From address domain.