Allow setting SPF/DKIM/DMARC to prevent mail spoofing when self hosting

[mildredboink05]

Please describe your feature request:

I self host interactsh and I would like to prevent anyone from spoofing emails from the domain that I use for interactsh. To do so, I'd like to set the following records

; SPF
example.com. IN TXT "v=spf1 -all"

; DKIM
*._domainkey.example.com. TXT "v=DKIM1; p="

; DMARC
_dmarc.example.com. IN TXT "v=DMARC1;p=reject;sp=reject;adkim=s;aspf=s"

See the following article for more details: https://www.cloudflare.com/learning/dns/dns-records/protect-domains-without-email/

Describe the use case of this feature:

Prevent email spoofing when self hosting

[GeorginaReeder]

Thanks for your feature request @mildredboink05 , we'll take a look into this!