What is an A (Address) record?

An A record (Address record) maps a domain name to an IPv4 address:

tidalmail.com A 192.0.2.1

Purpose: When someone visits tidalmail.com, DNS returns 192.0.2.1, and the browser connects there.

Email relevance:

MX records point to hostnames, which need A records to resolve to IPs.

Webmail interfaces need A records for browser access.

Some authentication uses A record lookups for IP verification.

A records are fundamental. Almost every DNS lookup eventually resolves to an A (or AAAA) record.

The A record is the GPS coordinates. Every destination name eventually resolves to actual coordinates.