If your domain will NEVER send e-mail out, you only really need and SPF record to tell other servers to drop e-mail FROM your domain. Even that’s somewhat optional. If you ever plan on sending ANY outbound (you should at very least for the occasional ticket) then do DKIM, DMARC and SPF. The more of these you do, the less likely e-mails FROM your domain are to be flagged as spam.
If your domain will NEVER send e-mail out, you only really need and SPF record to tell other servers to drop e-mail FROM your domain. Even that’s somewhat optional. If you ever plan on sending ANY outbound (you should at very least for the occasional ticket) then do DKIM, DMARC and SPF. The more of these you do, the less likely e-mails FROM your domain are to be flagged as spam.