Deliverability is not one setting — it is a stack of small decisions that compound. Miss the bottom of the stack and nothing above it matters. Work top to bottom.

1. Authentication

Publish all three records before you send a single email: SPF to say who can send, DKIM to sign each message, and DMARC to set the policy and collect reports. SignalMail's Deliverability page checks all three against live DNS.

2. Domain and inbox setup

Send cold email from a separate domain, never your primary — a burned reputation should not touch your main brand.
Redirect the sending domain to your main site so links resolve.
Connect each mailbox over OAuth where possible; credentials are encrypted at rest.

3. Warm up before volume

A brand-new mailbox has no reputation. Start with a handful of sends a day and ramp gradually over two to three weeks before running real campaign volume through it.

4. List hygiene

Verify every address before sending — invalid addresses spike your bounce rate.
Suppress hard bounces permanently so you never hit them twice.
Honor unsubscribes automatically; SignalMail adds a one-click unsubscribe footer to every send.

5. Content and volume

Keep messages plain and human, go easy on links and images, and spread sends across mailboxes under each one's daily cap — see multi-mailbox rotation for how that works.

6. Monitor and react

Watch the rolling mailbox health score — below 40, SignalMail auto-pauses the inbox before it drags the others down. Read your DMARC aggregate reports for spoofing or alignment failures.

Run this list once at setup, then re-check the monitoring steps every week.

The cold email deliverability checklist