In terms of the set of records it would be all mail related DNS records such as MX, SPF, and DKIM.
I can see use cases for both copy these records and now manage them with Sympl; or to not touch them at all.
Either way, it the mail is hosted on an external service, then having a way to ensure that mails (e.g. crontab or WordPress) can be processed and pushed through to the external service.