Email Deliverability & Domain Warmup: The Complete Guide

Why does email deliverability matter?

Deliverability decides revenue before your copy is ever read. A 10% inbox drop costs you roughly 10% of email revenue, and mail that hits the spam folder goes unread 95% of the time. Damaged reputation takes 4 to 8 weeks to recover, so protecting inbox placement is the whole game.

You can write the best emails in the world. If they land in spam, none of it matters.

Problem	Impact
10% inbox drop	~10% revenue loss
Spam folder	95%+ never get read
Blacklisting	Can't reach subscribers
Damaged reputation	4-8 weeks to recover

The short version

Set up SPF, DKIM, and DMARC before your first send. If you are on a new domain or spiking volume, warm up gradually over 5 to 6 weeks, starting at 500 to 1,000 sends a day to your most engaged subscribers and scaling to 20,000+. Watch open rate (target 40%+), bounce rate (under 0.5%), and spam complaints (under 0.05%). If you are already in spam, pause, clean the list, and re-warm slowly. Patience wins.

What determines whether your email lands in the inbox?

Four factors decide it. Sender reputation is your track record with providers, built over time. Email authentication (SPF, DKIM, DMARC) proves you are authorized to send. List quality covers engagement, bounces, and complaints. Content covers spam triggers and formatting. Reputation carries the most weight, but all four matter.

Sender Reputation

Email Authentication

List Quality

Content

Sender Reputation. Your track record with email providers. You build it over time through consistent, engaged sending.

Email Authentication. SPF, DKIM, and DMARC records that prove you are authorized to send from your domain.

List Quality. Engagement rates, bounce rates, spam complaints. Low engagement means deliverability problems, fast.

Content. Spam trigger words, formatting, HTML quality. This matters less than reputation, but it still matters. If you are already seeing problems here, dig into why your emails land in spam.

How do you set up SPF, DKIM, and DMARC?

Configure all three records at your DNS provider before you send a single marketing email. SPF lists the IPs allowed to send for you. DKIM adds a signature that proves your mail was not tampered with. DMARC tells servers what to do when authentication fails. Start DMARC on monitoring, then tighten. For a deeper walkthrough, see our guide to SPF, DKIM, DMARC, and BIMI.

SPF (Sender Policy Framework)

Tells receiving servers which IPs are allowed to send on your behalf.

Type: TXT
Host: @
Value: v=spf1 include:klaviyo.com ~all

DKIM (DomainKeys Identified Mail)

Adds a digital signature that proves your emails were not tampered with in transit.

Type: CNAME
Host: k1._domainkey
Value: dkim.klaviyo.com

DMARC (Domain-based Message Authentication)

Tells servers what to do when authentication fails. Start with monitoring, then tighten.

Type: TXT
Host: _dmarc
Value: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com

How do you warm up a new sending domain?

Warm up over 5 to 6 weeks. Start at 500 to 1,000 sends a day to your most engaged 30-day openers, then roughly double weekly: 2,000 to 3,000 in week 2, 5,000 to 7,000 in week 3, 10,000 to 15,000 in week 4, and 20,000+ by weeks 5 to 6. Skip this and you land in spam.

New domain, or a big jump in volume? You must warm up gradually.

Week 1

500-1,000 daily

Your most engaged only, 30-day openers. Run 3 campaigns a week.

Week 2

2,000-3,000 daily

Your 30-day engaged segment. Run 3 to 4 campaigns a week.

Week 3

5,000-7,000 daily

Your 30 to 60 day engaged. Run 4 campaigns a week.

Week 4

10,000-15,000 daily

Your 60 to 90 day engaged. Run 4 to 5 campaigns a week.

Week 5-6

20,000+ daily

Your full sendable list, back to normal cadence.

Critical Warning

Do not skip warmup. Blast high volume from a new domain and you land in spam. Recovery then takes 4 to 8 weeks.

What metrics should you watch during warmup?

Track four numbers on every send. Keep your open rate at 40% or higher, click rate at 5% or higher, bounce rate under 0.5%, and spam complaints under 0.05%. Red flags are opens below 25%, clicks below 2%, bounces above 2%, and complaints above 0.1%. Hit a red flag and you slow down.

Metric	Target	Red Flag
Open Rate	40%+	Below 25%
Click Rate	5%+	Below 2%
Bounce Rate	Under 0.5%	Above 2%
Spam Complaints	Under 0.05%	Above 0.1%

How do you maintain sender reputation over time?

Three habits keep you in the inbox. Practice list hygiene: remove hard bounces and suppress 180+ day inactives every quarter. Manage engagement: segment by engagement level, make unsubscribe easy, and hold complaints under 0.1%. Watch your content: skip spam triggers, keep a healthy text-to-image ratio, and use one consistent From name.

List Hygiene:

Remove hard bounces, automatic in most ESPs
Suppress 180+ day inactives every quarter
Verify any imported list before you import it

Engagement Management:

Segment by engagement level
Make the unsubscribe easy to find
Keep complaint rates under 0.1%
Send content people actually want

Content:

Skip spam triggers like "FREE!!!" and excessive caps
Keep a healthy text-to-image ratio
Include a plain text version
Keep one consistent "From" name

How do you recover from a spam folder problem?

Recovery takes about 6 weeks. Week 1, stop the bleeding: pause campaigns and send only to 30-day engaged at 500 to 1,000 a day. Week 2, clean the list: remove 90+ day inactives and verify through NeverBounce or ZeroBounce. Weeks 3 to 6, re-warm slowly and only scale when metrics stay healthy.

Already in spam? Here is the plan.

Week 1: Stop the Bleeding

Pause all campaigns
Send to 30-day engaged only
Drop to 500 to 1,000 daily

Week 2: Clean the List

Remove 90+ day inactives
Run the list through verification, NeverBounce or ZeroBounce

Weeks 3-6: Re-Warmup

Follow the warmup schedule above
Start with your most engaged 500 to 1,000
Only scale when metrics stay healthy

Ongoing: Monitor

Check Google Postmaster daily
Watch the open rate on every send
Do not rush. Patience is the whole game here.

What tools should you use to monitor deliverability?

Three tools cover it, two of them free. Google Postmaster Tools shows exactly how Gmail views your domain, including spam rate and reputation. Your ESP analytics put opens, bounces, and complaints in one place. MXToolbox checks your blacklist status and verifies your authentication records. Check Postmaster daily during warmup or recovery, and build a habit of monitoring your deliverability before it tanks.

Google Postmaster Tools (Free). See exactly how Gmail views your domain: spam rate, reputation, and more.

Your ESP Analytics. Open rates, bounces, and spam complaints in one place.

MXToolbox (Free). Check blacklist status and verify your authentication records.

Should you use a dedicated or shared sending domain?

Use shared until you are sending 50,000+ a month. Shared needs no warmup and is easier to set up, but your reputation is tied to other senders. A dedicated domain gives you full control over reputation and works better at scale, but it needs a 4 to 6 week warmup and more technical setup. Volume decides.

Shared Domain (Default)

No warmup required
Easier to set up
Your reputation is tied to others
Good for lower volumes

Dedicated Domain

Full control over your reputation
Needs a 4 to 6 week warmup
More technical to set up
Better for 50,000+ a month

Checklist

One-Time Setup:

Ongoing:

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