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Variable Envelope Return Path (VERP)

The use of a VERP address is an industry standard practice and improves the deliverability of outbound messages to major email service providers.

What Is A Return Path?

Email messages contain two "from" addresses, the Return Path and the Friendly From address.

 The Return Path address is also known as the Mail From, Envelope From, 5321.from, or the Bounce address. This address is not shown to the recipient. It is  an email address specified during the SMTP protocol communication process that determines where the receiving mail server sends back its bounce messages.

The Friendly From address is also known as the Display From or 5322.from. This is the address that is shown to a recipient.

What is a Variable Envelope Return Path?

A Variable Envelope Return Path, or VERP, address, is a custom return path address that allows SocketLabs to capture, analyze, process, and report upon bounces for any outbound mail sent on our platform. We encode unique data about each outbound message into an address, and will use that in the MAIL FROM protocol command.

An example of a VERP address is:


What are the benefits of VERP addresses?

The use of a Variable Envelope Return Path allows the SocketLabs On-Demand platform to better interpret message failures and provide more accurate details about each failure individually. It also allows for us to provide a single centralized location to view and access the information about all outbound messages processed through the account.

Additionally, the use of a VERP address enables SocketLabs to ensure that all outbound messages delivered through our network pass SPF authentication checks at their delivery point. 

What values are encoded into the VERP address?

To provide the most specific details about the bounce messages that come back to us, we encode the following details into the return path address:

  • SocketLabs Server ID
  • Recipient Address
  • Custom Mailing ID
  • Custom Message ID

The use of both Mailing and Message ID values in the encoded return path address means that it is beneficial to keep these values as short as possible. A return path address over 64 characters may impact deliverability. SocketLabs recommends keeping the combined total character count of these values to less than 30 total characters.

For further information, see: Message & Mailing/Campaign IDs

Can VERP Encoding Be Disabled For My Server/Account?

SocketLabs does not disable the use of a VERP address across an entire account or server. If VERP must be disabled for a specific domain, please contact our Support team for assistance.

Is There Anything Else I Should Know?

If you are concerned about no longer receiving bounce messages to your own addresses, please see our knowledge base article that details options for receiving forwarded copies of bounces and non-delivery reports: How SocketLabs Handles Non-Delivery Reports & Bounces.

E-Fax services often authenticate messages using SPF and the return path address. Users may experience issues sending outbound e-fax messages through SocketLabs On-Demand and should contact support to ensure the use of VERP is disabled to the domain of your e-fax service provider.