Domain & Instantly Email Setup

I need a hand finishing the technical side of my outbound email stack. I purchased the new domains and need help with configuring DNS, DMARC, MX, SPF, DKIM for reliable delivery and full compatibility with Instantly. I have 3 domains and would like to have 18 total emails addresses for sending cold emails via campaigns through Instantly.

Here’s what a successful hand-off looks like:
• All 18 mailboxes live, tested and able to send/receive.
• Domain DNS updated with correct MX, SPF, DKIM and DMARC records, fully propagating.
• Each mailbox connected inside Instantly, verified, and ready for campaigns (custom tracking domain included).
• Clear, step-by-step notes so I can reproduce the process for future addresses.