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

Results formx.eu.sendgrid.net

Resolver

Location

A

Name	TTL	Value
mx.eu.sendgrid.net	60	3.66.153.97AWS EC2 (eu-central-1) / Amazon Technologies Inc.
mx.eu.sendgrid.net	60	18.159.125.37AWS EC2 (eu-central-1) / Amazon.com, Inc.
mx.eu.sendgrid.net	60	18.196.11.73AWS EC2 (eu-central-1) / Amazon Technologies Inc.
mx.eu.sendgrid.net	60	34.241.228.115AWS EC2 (eu-west-1) / Amazon Technologies Inc.
mx.eu.sendgrid.net	60	52.16.69.42AWS EC2 (eu-west-1) / Amazon.com, Inc.
mx.eu.sendgrid.net	60	54.228.124.104AWS EC2 (eu-west-1) / Amazon.com, Inc.