Email deliverability — SPF, DKIM, DMARC

The DNS records, warmup pattern and content rules that get your email into the inbox.

The three records every sender needs

1. SPF

SPF says which servers may send mail for your domain. Add a single TXT record at the apex of your sending domain. If you only send through your provider, it will look like:

v=spf1 include:_spf.google.com ~all

Multiple providers? Include each one and end with ~all (soft-fail) or -all (hard-fail).

2. DKIM

DKIM cryptographically signs every outgoing message. Your SMTP provider (Gmail Workspace, SES, SendGrid, Mailgun, etc.) gives you a TXT record to add at selector._domainkey.yourdomain.com. Add exactly what they show — do not edit it.

3. DMARC

DMARC tells receivers what to do when SPF/DKIM fail and where to send reports. Start in monitor mode:

v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; pct=100

After a few weeks of clean reports, tighten to p=quarantine and eventually p=reject.

Warming a new sending domain

A brand new domain has zero reputation. Ramp up gradually so receivers learn your traffic is legitimate.

Days 1–3: 50 messages/day to your most engaged contacts
Days 4–7: 200/day
Week 2: 1,000/day
Week 3–4: 5,000+/day, then full volume

Stop ramping if your open rate drops below ~10% or your bounce rate exceeds 2% — that means receivers are pushing back.

Content rules that move the needle

Always include a plain-text alternative. RAPID SMTP does this automatically when you fill the plain-text body.
Keep image-to-text ratio reasonable. An email with one giant image and no text is almost guaranteed to land in spam.
Don't shorten URLs with bit.ly / t.co. Use your own domain.
Include a real physical address in the footer (CAN-SPAM & PECR requirement).
Include a working unsubscribe link — we add the List-Unsubscribe header for you, but the visible link in the footer matters too.

Monitor what receivers see

Google Postmaster Tools — domain & IP reputation for Gmail.
Microsoft SNDS — reputation for Outlook / Hotmail.
mail-tester.com — a quick score (out of 10) before you launch a campaign.
RAPID SMTP → Analytics — bounce, complaint and open trends per SMTP account.

When deliverability drops

Pause sending, look at the last 7 days of bounces in Email logs, and prune any list segments with low engagement. Then resume at half your previous volume.

Deliverability