I was trying to follow instruction and I thought configuring spf policy was a "requirement" after installation by reading iRedMail documentation.
May I make things clear?
SPF is simply a DNS record (TXT type), other mail servers will query your SPF record to see whether the email sent from "@your_domain.com" (in mail header "From:") is allowed or not. No addition setup required.
The same as above, to verify sender on iRedMail server, we use Amavisd with perl module perl-Mail-SPF.
Are you saying SPF verification is optional and not necessary?
Yes, but strongly recommended.
In that case, do I need to delete DNS records for SPF verification as well?
Please keep your SPF record.
Are you also saying Amavisd in iRedMail includes SPF verification feature so I do not have to configure it at all?
Yes, used to verify sender. But you still need SPF record to help others identity emails from your domain.
Please check what SPF is used for first (with Google).
Hope it's clear now.