Email depends on a few DNS records that rarely get day-to-day attention: MX for routing, SPF for who may send, DKIM for signatures. A tidy CMS migration or CDN cutover can overwrite them without anyone intending to touch mail.
Before you publish DNS changes, capture the current MX, TXT (SPF), and DKIM selectors. After the change, run the same lookups and compare.
Watch TTL. Low TTL helps rollbacks, but cached resolvers still lag. Plan a verify window, not only a deploy window.
If mail matters to the business, monitor those records the same way you monitor uptime - so a silent TXT edit is an alert, not a support ticket two days later.