Warm up your Customer.io sending domain
Warmy sends and engages with human-like conversations from your domain, so Gmail, Outlook and Yahoo learn to trust your campaigns before your next Customer.io send.
Customer.ioWarmy Keeps Customer.io Emails Out Of Spam And Promotions
Warmy connects to your Customer.io sending domain to warm it up automatically, validate SPF, DKIM and DMARC, monitor reputation and blocklists, and show exactly where your campaigns land across Gmail, Outlook and Yahoo, before you press send.
Connects To Customer.io In Under 25 Seconds | No Credit Card Required
- Senders
- 7,000+Senders
- Average inbox placement
- 98%Average inbox placement
- Human deliverability support
- 24/7Human deliverability support
Trusted By 7,000+ Ecommerce And B2B Senders
Loved By Thousands Of Marketers Around The World
The platform’s warmup processes make sure that our cold emails don’t bounce into spam filters. It also makes use of AI behavior tracking as we’re sending which is great for campaigns scaling. It’s also really valuable to be able to track open rates and responses.
Allan BlackSenior Affiliate & Strategic Partnerships Manager
Setup in under 25 seconds
Connect Customer.io To Warmy In Less Than 25 Seconds
No code, no migration, no change to how your team works in Customer.io. Three clicks and Warmy starts protecting the domain your campaigns are sent from.
- 01
Pick Customer.io
Choose Customer.io from the provider list inside Warmy - no developer, no API tinkering.
- 02
Connect your sending domain
Paste the sending address Customer.io uses. Warmy checks SPF, DKIM and DMARC instantly.
- 03
Press start
Warm-up, inbox-placement tests and reputation monitoring begin on the same day.
What Warmy Fixes For Customer.io Senders
Customer.io sends the campaign. Warmy makes sure it reaches the inbox.
See where Customer.io campaigns land
Seed-list tests place your real Customer.io template in live mailboxes and show inbox, promotions or spam for every provider - before you press send.
Monitor reputation and authentication
Continuous checks on SPF, DKIM, DMARC, blocklists and Google Postmaster data, with alerts the moment your Customer.io domain starts slipping.
Customer.io authentication
How To Authenticate Your Customer.io Sending Domain
Customer.io triggers lifecycle messaging from product and behavioural data. Gmail, Yahoo and Microsoft require authenticated email from bulk senders, so a verified sending domain with valid SPF, DKIM and DMARC is the baseline for reaching the inbox.
- 01Open Customer.io with an account that has administrator access.
- 02Go to Workspace Settings → Email → Sending domains.
- 03Add the sending subdomain you want to use, for example send.example.com.
- 04Copy the DNS records Customer.io generates - typically CNAME records generated by Customer.io.
- 05Publish each record with your DNS provider, exactly as shown.
- 06Return to Customer.io and run verification once DNS has propagated.
- 07Publish a DMARC TXT record at _dmarc.example.com, starting with p=none.
- 08Send a test message and confirm spf=pass, dkim=pass and dmarc=pass.
| Protocol | Purpose | Typical record | What it verifies |
|---|---|---|---|
| SPF | Authorizes sending infrastructure | TXT record on the sending domain | The sending server |
| DKIM | Adds a cryptographic signature | CNAME records generated by Customer.io | The message and the signing domain |
| DMARC | Defines alignment and failure policy | TXT record at _dmarc | The visible From domain |
Record names and values differ per account. Always copy them from your own Customer.io screen rather than from a generic example.
Why placement drops
Why Customer.io Emails Go To Spam Or Promotions
Authentication only proves who sent the message. Placement depends on reputation, engagement and list quality - and Customer.io senders hit a few specific problems.
Event-driven campaigns can fire far more messages than planned when a data pipeline misbehaves.
Product, lifecycle and marketing streams often share one domain and one reputation.
New workspaces start sending at production volume on day one.
Common causes across every sender
- A cold sending domain pushed to full volume in a single campaign.
- Invalid, purchased or long-inactive addresses raising bounce and complaint rates.
- Weak or missing DMARC alignment between the signing domain and the From address.
- Blocklist entries or a damaged IP reputation nobody is monitoring.
- Image-heavy, discount-heavy templates that filters cluster into promotions.
Customer.io Deliverability Checklist
- Verified sending domain configured and verified
- Only one SPF record per hostname, under the 10-lookup limit
- DKIM records published and passing
- DMARC record live and monitored
- SPF or DKIM aligned with the visible From domain
- Sending domain warmed up gradually
- Google Postmaster Tools connected
- Blocklists checked continuously
- Inbox-placement test run before major campaigns
- Inactive and invalid recipients suppressed
Warmy for Customer.io senders
Test Your Customer.io Deliverability With Warmy
Passing SPF, DKIM and DMARC confirms authentication, but it does not reveal where your campaigns actually land. Warmy helps Customer.io senders test inbox placement across major providers, monitor domain reputation, identify blocklist issues and detect authentication problems before a campaign is sent.
Inbox placement testing
See the inbox, promotions and spam split per provider before you press send.
Domain reputation monitoring
Track reputation, blocklists and authentication changes continuously.
Automated warm-up
Build reputation on a new Customer.io sending subdomain with human-like activity.
Deliverability experts
Certified specialists review your setup and prioritize what to fix first.
FAQCustomer.io Deliverability
Customer.io Deliverability
Frequently Asked Questions
Yes. Warmy connects to the domain and mailboxes you send from with Customer.io in under 25 seconds. You select Customer.io in the provider list, connect your sending domain, and warm-up, placement testing and monitoring start the same day.
The most common causes are a cold sending domain, incomplete SPF, DKIM or DMARC alignment, poor list quality and low engagement. Event-driven campaigns can fire far more messages than planned when a data pipeline misbehaves. Warmy identifies which of these applies to your domain and fixes reputation automatically.
Create a verified sending domain under Workspace Settings → Email → Sending domains, publish the DNS records Customer.io generates (CNAME records generated by Customer.io), add a DMARC TXT record at _dmarc.yourdomain.com and verify. Warmy validates all three records for you and flags anything that fails.
Yes. A domain with no sending history has no reputation, and mailbox providers filter unknown senders aggressively. Warmy warms the domain up automatically with human-like conversations until it can carry your full Customer.io volume.
Yes. Warmy's seed list places your real Customer.io template into live mailboxes and reports inbox, promotions or spam placement per provider, including Gmail, Outlook, Yahoo and corporate Microsoft 365 accounts.
No. Warmy works alongside Customer.io. Your campaigns, flows and templates stay exactly where they are - Warmy only improves and monitors the reputation of the domain and mailboxes you send from.
Most senders see measurable placement improvements within two to three weeks of continuous warm-up, and authentication problems are fixed as soon as the records are corrected. Domains with existing reputation damage take longer.
Yes. Run Warmy's free email deliverability test to see your current inbox placement, authentication status and blocklist standing before you start a trial.
Keep going
Related Warmy Tools And Guides
- Run an inbox placement test
- Check your SPF record
- Generate and monitor DMARC
- Email domain warm-up
- Deliverability insights and monitoring
- Email deliverability guide
Last reviewed August 2026 by Daniel Shnaider, Warmy Co-Founder, email deliverability specialist, for Customer.io senders.
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Where Your Customer.io Emails Land
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