Use a domain you own or a public domain for passive DNS inspection.

MX

Query the domain’s MX records and note preference and hostname.

Addresses

Resolve each MX hostname to A and AAAA records.

SPF

Query TXT at the sending domain and identify the SPF policy.

DMARC

Query TXT at _dmarc.example.com.

DKIM

You need a selector. Take s= and d= from a real DKIM-Signature, then query:

selector._domainkey.signing-domain

What to write down

For every lookup, keep the queried name, record type, answer, TTL and which resolver or authoritative server answered.

Reference material