Email Specs
Email Deliverability Checklist
Deliverability is mostly an infrastructure problem that marketers inherit. This is the checklist I run before any new sending domain goes live, and again whenever inbox placement drops.
| Record | What it does | Status for bulk senders |
|---|---|---|
| SPF | Authorizes sending IPs for your domain | Required |
| DKIM | Cryptographically signs your messages | Required |
| DMARC | Tells receivers what to do on failure | Required, p=none is acceptable to start |
| Reverse DNS | Maps sending IP back to a hostname | Required for your own IPs |
| TLS on transmission | Encrypts the connection | Required |
| Requirement | Detail |
|---|---|
| Applies to | Senders of roughly 5,000 or more messages per day to those providers |
| One click unsubscribe | List-Unsubscribe and List-Unsubscribe-Post headers |
| Unsubscribe processing | Honoured within 2 days |
| Spam complaint rate | Keep below 0.3 percent, aim under 0.1 percent |
| Domain alignment | From domain must align with SPF or DKIM |
| Check | Target |
|---|---|
| Hard bounce rate | Under 2 percent |
| Inactive suppression | Suppress after 6 to 12 months of no engagement |
| Purchased lists | Never send to them |
| Plain text alternative | Always include a text part |
| Link domains | Use your own tracking domain, avoid public shorteners |
| New domain warmup | Ramp volume over 4 to 6 weeks |
Notes
Authentication gets you eligibility, engagement gets you the inbox. Once SPF, DKIM and DMARC pass, the variable that determines placement is how recipients behave: opens, replies, moves out of spam, and above all the absence of complaints. Sending less to people who want it beats sending more to everyone.
The single highest impact hygiene change most senders can make is suppressing long term inactives. It feels like shrinking the list, but complaint rate and spam trap risk both concentrate there, and inbox placement for the remaining audience typically improves within a few sends.
Complaint rate is a hard ceiling, not a soft target. Gmail's threshold is 0.3 percent and crossing it can throttle an entire domain's mail, so put a visible unsubscribe link at the top as well as the bottom. People who cannot find unsubscribe press the spam button instead.
Provider requirements have tightened repeatedly since the 2024 Gmail and Yahoo changes, and enforcement details continue to evolve. Read Google's sender guidelines and Yahoo's postmaster documentation directly before making infrastructure decisions.
Frequently asked questions
Do I need DMARC if I already have SPF and DKIM?
Yes. Bulk senders to Gmail and Yahoo are required to publish a DMARC policy. Starting at p=none lets you collect reports without affecting delivery, then tighten once alignment is clean.
How do I know if I am in spam?
Seed testing across major providers, plus Google Postmaster Tools for Gmail specific reputation and complaint data. Open rate alone will not tell you, especially with Apple's privacy protection inflating it.
Should I use a subdomain for marketing email?
Yes. Sending marketing from a subdomain isolates its reputation from your transactional and corporate mail, so a bad campaign does not take down your invoices.
Official sources
Platforms change specifications without notice. Check the primary documentation before a launch that depends on an exact value.
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