Marketing

Customer.io

Customer.io is built around event-driven workflows rather than scheduled campaigns. Authentication uses standard DKIM/SPF on a sending subdomain plus a return-path CNAME.

DNS records to publish

Type	Host	Value
CNAME	cio<id>._domainkey	`dkim.customeriomail.com` DKIM
CNAME	bounces	`bounce.customeriomail.com` Custom return-path

Authentication setup

SPF

Add include:mail.customeriomail.com to SPF on the sending subdomain.

DKIM

Publish the CNAME Customer.io generates.

DMARC

Standard rollout; transactional-style traffic typically reaches p=reject quickly.

Deliverability tips

Use event-driven sends rather than weekly broadcasts to maintain high engagement signals.
Configure suppression rules on bounces and complaints inside Customer.io so suppressed contacts don't re-enter campaigns.
Verify both the sending subdomain and the bounce subdomain are authenticated; missing the bounce CNAME breaks SPF alignment.

Customer.io setup docs

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