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

Results formd3.expression.com

Domain Name	First seen	Still exists
ww25.mailserver.md3.expression.com	2025-07-29T04:48:45.517Z
ww16.mailgw.md3.expression.com	2025-05-28T11:38:21.679Z
ww25.mx.md3.expression.com	2025-01-31T01:23:49.643Z
ww25.auth.md3.expression.com	2025-01-29T06:49:25.864Z
ww25.mailgate.md3.expression.com	2024-11-01T10:23:06.850Z
ww38.md3.expression.com	2024-09-13T06:21:32.177Z
ww38.smtpauth.md3.expression.com	2024-09-12T08:41:53.520Z
ww25.m.md3.expression.com	2024-08-02T07:58:53.704Z
ww25.pop3.md3.expression.com	2024-08-01T12:33:25.814Z
*.md3.expression.com	2024-07-22T18:44:07.527Z
ww38.mailserver.md3.expression.com	2024-07-13T23:45:51.489Z
ww38.mailgate.md3.expression.com	2024-07-13T23:45:48.144Z
ww38.mailgw.md3.expression.com	2024-07-13T23:45:47.543Z
ww38.m.md3.expression.com	2024-07-13T23:35:31.739Z
ww38.ns2.md3.expression.com	2024-07-13T23:25:44.205Z
ww38.mx.md3.expression.com	2024-07-13T22:11:54.264Z
ww38.pop3.md3.expression.com	2024-07-13T21:55:29.166Z
ww38.auth.md3.expression.com	2024-07-13T18:30:45.453Z
ww16.md3.expression.com	2022-05-14T01:13:06.447Z