The Email Deliverability Checklist for 2026

A perfectly designed email is worthless if it lands in spam. Deliverability — whether your message reaches the inbox — depends on three things: who you are (authentication and reputation), who you send to (list quality and engagement) and what you send (content and code).

Since early 2024, Gmail and Yahoo have enforced stricter rules for bulk senders, and other mailbox providers have moved in the same direction. This checklist covers what to verify before you send.

1. Authenticate your domain

Authentication proves you are allowed to send from your domain.

• SPF lists the servers permitted to send mail for your domain. Keep it under the 10-DNS-lookup limit.
• DKIM signs each message so receivers can verify it wasn't altered. Use your own domain in the signature, not only your provider's.
• DMARC tells receivers what to do when SPF or DKIM fail, and sends you reports. Gmail and Yahoo require a DMARC record for bulk senders; start with p=none to monitor, then move toward quarantine or reject.
• Alignment — the domain in your From address should match the domain authenticated by SPF or DKIM.

2. Make unsubscribing easy

• Include a visible unsubscribe link in every marketing email.
• Support one-click unsubscribe with the List-Unsubscribe and List-Unsubscribe-Post headers; Gmail and Yahoo require this for bulk senders.
• Process unsubscribes promptly — Gmail and Yahoo expect it within two days.
• Include a physical postal address; laws like CAN-SPAM require it for commercial email.

KLinh Preflight's legal checks flag missing unsubscribe links and address placeholders, including platform tags such as Salesforce's unsubscribe center link.

3. Keep complaints low

Gmail asks bulk senders to keep their spam complaint rate below 0.3%, and recommends staying well under 0.1%. Monitor it in Google Postmaster Tools.

• Only send to people who opted in.
• Set expectations at sign-up about frequency and content.
• Make sure the sender name is recognizable.

4. Clean your list

• Remove hard bounces immediately.
• Suppress addresses that haven't engaged in a long time, or run a re-engagement campaign first.
• Never buy lists.
• Use double opt-in where practical to avoid typos and spam traps.

5. Check content and code

Mailbox filters look at the message too. Common problems:

• Broken or suspicious links. Empty links, missing protocols and mismatched link text erode trust.
• Image-only emails. Give images alt text and include real HTML text.
• Heavy HTML. Gmail clips messages over about 102 KB, hiding your footer — and possibly the unsubscribe link. See why Gmail clips emails.
• Raw merge tags. A visible {{ first_name }} looks careless and can hurt engagement.
• Missing preheader. Inbox previews then fill with stray text like "View in browser".

6. Warm up new domains and IPs

Sudden volume from a new domain or IP looks suspicious. Increase volume gradually and start with your most engaged subscribers.

7. Monitor after you send

• Watch bounces, complaints and unsubscribes per campaign.
• Review DMARC reports for unauthorized senders.
• Treat open rates carefully: Apple Mail Privacy Protection preloads images, which inflates opens. Clicks and conversions are more reliable.

Quick pre-send checklist

1. SPF, DKIM and DMARC pass and align.
2. One-click unsubscribe headers are set by your ESP.
3. Visible unsubscribe link and postal address are in the email.
4. Subject line and preheader are set.
5. No empty links, missing protocols or raw merge tags.
6. All images have alt text.
7. HTML size is safely under 102 KB.
8. The list is opted-in and cleaned.

Steps 3 to 7 can be checked automatically. Create a campaign in KLinh Preflight and paste your HTML to see them in seconds. Authentication and list health are set up in your DNS and ESP.