Gitbook uses Customer.io

Gitbook uses Customer.io as their primary email service provider. They rank #7,037 in the Tranco list of most-popular domains. Their email authentication setup is good (score 80/100).

Marketing ESP

Customer.io

Total observations6

Active days4

Avg per active day1.5

Last activity📬 Active · 4 days ago

Cadence~weekly

Other technologies

Non-ESP tools detected in this brand's emails. Independent of who sends — a brand can use any combination.

HTML builder

Beefree SDK

Compare Gitbook with another brand:

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.

✓

Solid setup, room to improve

Most authentication signals are present. A couple of pieces would tighten things up.

80/100

SPF

pass

DKIM

pass

DMARC

pass (quarantine)

BIMI

none

Unsubscribe

one-click

SPF lookups 6/10

SPF / DKIM / DMARC above reflect the last 1 email we've observed. DMARC policy is read live from DNS.

Authentication

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

SPF alignment: all 6 observed emails use a return-path aligned with gitbook.com (cio72247.gitbook.com). SPF authenticates the visible From — supports DMARC directly.

DKIM alignment: all 6 observed emails sign with a domain aligned with gitbook.com (cio72247.gitbook.com). DKIM authenticates the visible From — supports DMARC directly.

Other ESPs detected

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

None — only the primary ESP(s) shown above

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.

Customer.io ✓ via Mailgun

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

Mailgun

SendGrid

Probed: gitbook.com, cio72247.gitbook.com

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.

Folder	Count	Share
inbox	6	100.0%

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.

ESP	Emails	Placement	Inbox %	Tabs %	Spam %
Customer.io	6		100.0%	0.0%	0.0%

ESP activity over time

May 29 – Jun 26, 2026 · 4 days with sends

Last 30d Last 90d

By ESP By inbox/spam

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