Hi, TMail21 is a SaaS solution that can support many types of processes. It can support both internal as well as external processes and in particular it can also support approval processes.

Additionally it supports characteristics like Certified Mail, guaranteed delivery, non-spoofable identities, non-repudiable audit trails etc. which make it perfect for this kind of problem.

You can learn more at https://tmail21.com. This next link specifically talks about characteristics related to security, identity, non-repudiability, certified mail etc. https://tmail21.com/why-tmail/mission-critical-processes/