docker.io

docker.io · Last checked 2026-10-04 02:19 UTC

docker.io

Excellent: no problems found

docker.io scored 100/100 (grade A). No problems were found in the checks that ran. Detected senders: Google Workspace and Mailgun.

Checked 2026-10-04 02:19 UTC · fresh check

3 passed0 failing5 for informationDetected senders: Google Workspace, Mailgun

All checks

MXCan servers find your inbox?No issues foundPass

Nothing to report.

SPFWho may send as you?No issues foundPass

Nothing to report.

DKIMAre your emails signed?DKIM key publishedPass
  • Pass: DKIM key published

    docker.io publishes a DKIM key under google.

DMARCWhat happens to fakes?DMARC policy is quarantine; consider rejectInfo
  • Info: DMARC policy is quarantine; consider reject

    Failing mail goes to spam rather than being refused. When reports show no legitimate failures, reject gives the strongest protection.

    How to fix this
AlignmentDoes it match your From?SPF alignment depends on a custom Return-PathInfo
  • Info: SPF alignment depends on a custom Return-Path

    This is a heuristic. Your SPF record only authorizes third-party senders (mailgun.org, _spf.mailgun.org, _spf1.mailgun.org, _spf2.mailgun.org, _spf.eu.mailgun.org). By default they bounce from their own Return-Path domain, and SPF then passes for that domain, not docker.io. Even relaxed alignment needs the Return-Path's organizational domain to be docker.io, so set up a custom Return-Path (bounce) domain under docker.io with each provider, and sign with DKIM as docker.io.

BIMICan inboxes show your logo?No BIMI recordInfo
  • Info: No BIMI record

    No BIMI record at default._bimi.docker.io. BIMI is optional: it shows your logo next to your mail in supporting inboxes once DMARC is enforced.

    How to fix this
MTA-STSIs mail to you encrypted?No MTA-STS recordInfo
  • Info: No MTA-STS record

    No MTA-STS record at _mta-sts.docker.io. MTA-STS (RFC 8461) makes sending servers require TLS and a valid certificate when delivering to you, which blocks downgrade attacks.

    How to fix this
TLS-RPTWill you hear about failures?No TLS-RPT recordInfo
  • Info: No TLS-RPT record

    No TLS reporting record at _smtp._tls.docker.io. TLS-RPT (RFC 8460) tells senders where to send daily reports about failed encrypted deliveries to you.

    How to fix this

How to fix it

Strengthen the DMARC policyTXT

Rejects mail that fails DMARC, the strongest protection against spoofing.

TypeTXT
Name / Host
_dmarc.docker.io

Some DNS providers want just “_dmarc” here.

Value
v=DMARC1; p=reject; rua=mailto:q1xwnepx@ag.dmarcian.com; adkim=r; aspf=r
Replaces
v=DMARC1; p=quarantine; pct=100; rua=mailto:q1xwnepx@ag.dmarcian.com; ruf=mailto:q1xwnepx@fr.dmarcian.com;

Publish the MTA-STS recordTXT

Tells sending servers that docker.io publishes an MTA-STS policy at https://mta-sts.docker.io/.well-known/mta-sts.txt. Change the id whenever the policy file changes.

TypeTXT
Name / Host
_mta-sts.docker.io

Some DNS providers want just “_mta-sts” here.

Value
v=STSv1; id=202610040219

Host the MTA-STS policy filepolicy-file

Serve this file over HTTPS with a valid certificate for mta-sts.docker.io. It lists your MX hosts and starts in testing mode; switch to mode: enforce once TLS-RPT reports show no failures.

Location
https://mta-sts.docker.io/.well-known/mta-sts.txt
Contents
version: STSv1
mode: testing
mx: aspmx.l.google.com
mx: alt1.aspmx.l.google.com
mx: aspmx2.googlemail.com
mx: aspmx3.googlemail.com
mx: aspmx4.googlemail.com
mx: aspmx5.googlemail.com
max_age: 604800

Set up a TLS report addressinstruction

Sending servers will report TLS failures when delivering to docker.io, which you need before enforcing MTA-STS. The address must accept TLS reports; a DMARC report address does not necessarily do so.

Applies to: _smtp._tls.docker.io

  1. Pick an address that will receive TLS reports: a mailbox you read (for example tls-reports@docker.io, created first) or a TLS reporting service. 2. Publish a TXT record at _smtp._tls.docker.io with the value v=TLSRPTv1; rua=mailto:<that address>.

Prepare BIMIinstruction

BIMI shows your logo next to messages in supporting inboxes, but only for mail that passes DMARC under an enforced policy.

Applies to: default._bimi.docker.io

  1. Enforce DMARC first: p=quarantine or p=reject at 100% (no pct below 100). 2. Convert your logo to an SVG Tiny PS file and host it over HTTPS, for example https://docker.io/bimi/logo.svg. 3. For Gmail and Apple Mail, obtain a VMC or CMC certificate for the logo. 4. Publish a TXT record at default._bimi.docker.io with v=BIMI1, l= set to the logo URL and a= set to the certificate URL.