substack.com

Live email deliverability and anti-spoofing audit. Every value below was read from public DNS at the moment this page was generated.

91/100 — This domain is configured correctly for both sending and receiving. Accepts mail · Protected against spoofing · Hosted by Mailgun

Findings

spf

SPF ends in ~all (softfail); unauthorised mail is marked rather than rejected.
```
v=spf1 include:_spf.google.com include:mailgun.org include:mail.zendesk.com ~all
```
Fix: Move to -all once you have confirmed all senders are listed.
mta sts

No MTA-STS policy, so inbound mail can be downgraded to an unencrypted connection.

Fix: Publish _mta-sts.substack.com and host a policy at https://mta-sts.substack.com/.well-known/mta-sts.txt.
mx

Mail is handled by Mailgun.
```
10 mxa.mailgun.org, 10 mxb.mailgun.org
```

dmarc

DMARC is enforcing with p=reject.

v=DMARC1; p=reject; pct=100; rua=mailto:re+kvnosxqvppz@dmarc.postmarkapp.com; sp=reject; aspf=r;

MX	`10 mxa.mailgun.org` `10 mxb.mailgun.org`
SPF	`v=spf1 include:_spf.google.com include:mailgun.org include:mail.zendesk.com ~all`
DMARC	`v=DMARC1; p=reject; pct=100; rua=mailto:re+kvnosxqvppz@dmarc.postmarkapp.com; sp=reject; aspf=r;`
DKIM selectors	`google`
MTA-STS	not published
TLS-RPT	not published
BIMI	not published
DNSSEC	not validating

Run this check in your own code

Same data, as JSON, in one request. No SMTP probing, no stored recipient data, 250 free calls a month.

curl "https://mailgrade.dev/v1/domain?domain=substack.com"

Also available: /v1/verify?email=… for individual addresses, and /v1/verify/batch for lists.