Transaction Communication Messages for SalesOrder & Estimate

Hi,

I am sending out an email for the Sales Order. How can I also attach this email to the Estimate for a communication message?

I attempted to add it as a customRecord However, it did not work.

email.send({ author: recipientService.getAuthorId(), recipients: [customerEmail], bcc: recipientService.getFallbackRecipients(), subject: mergeResult.subject, body: mergeResult.body, attachments: [pdfFile], relatedRecords: { entityId: customer.id, transactionId: salesOrder.id, customRecord: { id: estimate.id, type: record.Type.ESTIMATE, }, }

I also tried attaching the message record to the Estimate and/or Sales Order. However, I received an error of Attaching of record type message to salesorder is not supported