Instantly doesn't actually do any of the sending - we send the email information to the email provider of the sending accounts you've connected, which then sends your emails.
You will not need to add any SPF/DKIM records for Instantly, but you will need to add them for your email provider (ESP). Please check your ESP's documentation to obtain the DNS records.
MX Record: MX record is known for directing emails to you. Without an MX Record, you won't be able to receive replies.
SPF record: SPF record specifies authorized domains to send emails. It helps reduce spam and phishing attempts and improves your email deliverability.
DKIM record: DKIM adds a signature to emails, making them easier to trace and preventing spoofing.
DMARC record: DMARC authenticates emails, letting the world know they were sent from a legitimate source.
You can click the Test domain setup option to verify if your DNS records are set up properly. Learn how to add the DNS records here.
Our servers (IPs) send information like when the email needs to be sent, what it needs to look like (including styling, variables, spintax) + things like the open tracking code using your custom tracking domain. This information is sent to the mail servers of your connected sending accounts, which then do the actual email sending.
We keep rotating our servers (IPs), that send over this information every few hours to ensure that the accounts themselves don't run into any reputation issues.