Email Detective — ESP Tracker

Customer

customer.io ↗

🏆Rank #2,290 🏷 SaaS 🇺🇸United States ✓ Inbox 99%

Customer uses Customer.io for marketing email and SendGrid for transactional/notifications. They rank #2,290 in the Tranco list of most-popular domains. We've also observed sends via 6 other providers: Salesforce CRM, Amazon SES, HubSpot, Intercom, Marketo, Mailgun. Email goes out from 2 different subdomains. Their email authentication setup is good (score 80/100). We've recorded 15 ESP changes since first observing this brand.

Marketing ESPCustomer.io

Transactional ESPSendGrid

Total observations1,638

Active days61

Avg per active day26.9

Last activity📬 Active · today

Cadence~weekly

Email setup 80/100

Authentication signals observed in this brand's emails. SPF, DKIM and DMARC are the standard sender-authentication stack — see the DMARC policy below for whether spoofing is actually blocked or just monitored. One-click unsubscribe meets Google & Yahoo's bulk-sender requirements.

SPF / DKIM / DMARC above reflect the last 10 emails we've observed. DMARC policy is read live from DNS.

DMARC reports sent to DMARC Digests. Policy p=quarantine means receivers actively block or quarantine spoofed mail.

SPF alignment: all 1242 observed emails use a return-path aligned with customer.io (em614.customer.io, cio1.customer.io, bounces.customer.io). SPF authenticates the visible From — supports DMARC directly.

DKIM alignment: all 1236 observed emails sign with a domain aligned with customer.io (customer.io, cio1.customer.io, tests.customer.io). DKIM authenticates the visible From — supports DMARC directly.

TLS: 72% TLS 1.3, 28% TLS 1.2 (across 540 sends).

Delivery: fast — 93% of emails in the last 7 days arrive in under 10 seconds (across 232 sends).

Other ESPs detected

Brands often use multiple ESPs (e.g. one for marketing, another for transactional/notifications).

Confirmed senders

ESPs we've seen sending email for this brand. Green = confirmed by SPF, sender IP rDNS, or known infra pairing (label shows the source). Grey = observed but not yet confirmed by SPF or PTR.

Amazon SES ✓ confirmed Mailgun ✓ confirmed SendGrid ✓ confirmed Customer.io ✓ via Mailgun Salesforce CRM ✓ via Salesforce MC Zendesk ✓ via sending IP

Other SPF authorizations

ESPs this brand has authorized in their SPF record. We confirm them with a green ✓ only after seeing recurring use (3+ emails across 2+ days). Until then they stay here — either we haven't observed any email yet, or we've seen a handful but not enough to call them a regular sender for the brand.

Google Workspace Mailchimp

Probed: customer.io, em1933.customer.io, bounces.customer.io, cio1.customer.io, em614.customer.io, tests.customer.io, cio1.login.customer.io, em908.customer.io, login.customer.io

Where emails landed (Gmail)

Folder distribution across all emails from this brand observed in Gmail inboxes. High inbox % = good deliverability; spam appearances are the headline signal.

Placement by ESP

Which ESP's emails are landing where. Sorted by spam % so problem senders surface first. Brands using one ESP for marketing and another for transactional often see very different placement profiles per ESP. Per-ESP folder data only started being captured recently — counts here may be smaller than the total above until backfill catches up.

Monthly observations per ESP. Brands often run multiple ESPs concurrently — marketing on one, transactional on another — so this chart shows usage rather than switches.

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Sending IPs

IP addresses customer.io has been observed sending from, and where their mail landed in Gmail.

Sending domains