Create, bind and deliver each message code safely
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1
Separate seal sales from email sending
The VerifySeal WISECP reseller module can sell and fulfil High Security seals, but it does not automatically modify every email sent by WISECP or WHMCS. Treat outbound email integration as a separate server add-on.
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2
Find the final mailer layer
Use a supported add-on or custom mail transport that can set the final Message-ID, change arbitrary message headers, update both HTML and plain-text bodies, and run before DKIM signing.
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3
Do not rely on a template hook
A pre-send template hook is insufficient unless the platform guarantees it controls the final Message-ID and headers. In WHMCS, EmailPreSend documents merge fields and attachments but not control of the final Message-ID.
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4
Keep the key in server configuration
Store the API key in protected module configuration or an environment variable. Do not place it in an email template, custom client field, theme or browser request.
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5
Make retries idempotent
Use the billing platform email log, queue ID or another stable send ID as the idempotency key. Persist the Message-ID and VEM result before handing the message to the transport.
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6
Test every message route
Test invoices, support mail, service notices and administrator-sent email separately. If the platform cannot preserve the chosen Message-ID, route High Security mail through a trusted gateway that can.