Experience suggests odds are pretty good your form broke sometime in the last couple of years anyway—bad address, broken form, misconfigured mailserver. Did you notice? Do you test it?
Oh yeah, and SPF! Another good one. Is your webserver’s mailserver in your SPF record? Does it sign with DKIM? Have you checked your DMARC reports lately?
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko