We currently do not have a docusign option for modifications. At the time we are mailing the NTB and needing it mailed back signed as the proof of the NTB being sent. We have thought about replacing this with certified mail as the certified mail receipt would be the proof since we are struggling to get NTBs back. Is there any best practices that wouldn't allow for this?

From the FAQs:

Examples of a record of receipt include: the borrower’s signed acknowledgment of receipt of the Notice of Special Flood Hazards; the borrower’s initials on a form that acknowledges receipt; the borrower’s electronic signature that acknowledges receipt, or a certified return receipt if the Notice of Special Flood Hazards was mailed to the borrower. Lenders may keep the record in the form that best suits the lender’s business practices. Lenders may retain the record electronically, but they must be able to retrieve the record within a reasonable time pursuant to a document request from their Federal supervisory agency.