It can be anything! An apex, subdomain, or even a URL.

Results forrelay2.mail.marketmatrix.com

Logged At	Not Before	Not After	Common Name	Matching Identities	Issuer Name
2025-07-18T21:14:05.195	2025-07-18T00:00:00	2026-07-17T23:59:59	relay2.mail.marketmatrix.com	relay2.mail.marketmatrix.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G2
2025-07-18T21:12:38.833	2025-07-18T00:00:00	2026-07-17T23:59:59	relay2.mail.marketmatrix.com	relay2.mail.marketmatrix.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G2
2021-01-29T08:10:43.311	2021-01-29T00:00:00	2022-01-29T23:59:59	relay2.mail.marketmatrix.com	relay2.mail.marketmatrix.com	C=US, O=DigiCert Inc, OU=www.digicert.com, CN=Encryption Everywhere DV TLS CA - G1