github.com email setup: SPF, DKIM, DMARC & tools

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Domain

github.com

The three core checks pass. What is missing is the transport and trust layer around them.

4 of 8 checks pass · 6 tools visible in DNS · nothing urgent

Grade C

SPFValid, soft fail20/20

DKIM7 keys found15/15

DMARCPartial (p=quarantine)22/30

MX1 host10/10

MTA-STSNot published0/10

TLS-RPTNot published0/5

BIMINot published0/5

DNSSECNot signed0/5

1 · Authentication and transport

SPF

PassValid, soft fail

Anything not on the list is accepted but marked. Google recommends ~all; with DMARC enforced it is as strong as -all.

v=spf1 ip4:192.30.252.0/22 include:spf.protection.outlook.com include:_netblocks.google.com include:_netblocks2.google.com include:mail.zendesk.com include:_spf.salesforce.com include:servers.mcsv.net include:mktomail.com include:sendgrid.net ip4:62.253.227.114 ip4:166.78.69.169 ip4:166.78.69.170 ip4:166.78.71.131 ~all

8 DNS-lookup mechanisms — close to the limit of 10.

DKIM

Pass7 keys found

Selectors google, selector1, k1, k2, k3, s1, s2 publish a public key. 6 of them point at a vendor by CNAME.

google._domainkey, selector1._domainkey, k1._domainkey, k2._domainkey, k3._domainkey, s1._domainkey, s2._domainkey

DMARC

PassPartial (p=quarantine)

Failing mail goes to spam. One step from full enforcement.

v=DMARC1; p=quarantine; sp=reject; pct=100; rua=mailto:dmarc@github.com; ruf=mailto:dmarc@github.com; fo=1

MX

Pass1 host

One host, but it is a provider endpoint that is redundant behind the name.

10 github-com.mail.protection.outlook.com

MTA-STS

ReviewNot published

Sending servers cannot tell that this domain requires TLS, so inbound mail can be downgraded to plain text by anyone on the path.

TLS-RPT

OptionalNot published

Nobody is told when TLS to this domain fails. Cheap to add once MTA-STS is in place.

BIMI

OptionalNot published

DMARC is enforced, so this domain qualifies. Yahoo and Fastmail show the logo from the record alone; Gmail and Apple Mail also need a paid VMC or CMC certificate.

DNSSEC

OptionalNot signed

Optional. Signing the zone protects every record in this report from tampering.

2 · Tools visible in DNS

Layer	Tool	Evidence
Mailbox	Google Workspace	DKIM google._domainkey
Mailbox	Microsoft 365	MX github-com.mail.protection.outlook.com
Marketing	Mailchimp	SPF include:servers.mcsv.net
Marketing	Marketo	SPF include:mktomail.com
Transactional	SendGrid	SPF include:sendgrid.net
Support	Zendesk	SPF include:mail.zendesk.com

Only tools that leave a DNS trace appear. A shared DKIM selector is attributed only when its CNAME target names the vendor.

3 · Sender requirements (Google, Yahoo, Microsoft)

Requirement	Applies to	Status	Note
Authenticate with SPF or DKIM	GoogleYahooMicrosoft	Verified	At least one method is in place.
Bulk senders: both SPF and DKIM	GoogleYahoo	Verified	Both are present.
Publish a DMARC record (p=none is enough)	GoogleYahooMicrosoft	Verified	Policy is p=quarantine.
From: domain aligns with SPF or DKIM	GoogleYahooMicrosoft	Not checkable here	Needs a real message. The Send-a-Test report will check this.
Valid forward and reverse DNS for sending IPs	GoogleYahoo	Not checkable here	Depends on the sending server, not the domain.
Encrypt in transit (TLS)	GoogleYahoo	Not checkable here	Outbound TLS depends on your sending tool; MTA-STS would cover inbound.
One-click unsubscribe (RFC 8058) for marketing mail	GoogleYahoo	Not checkable here	A message header, not a DNS record. Microsoft recommends it rather than requiring it.
Spam complaint rate under 0.1% (0.3% is the hard limit)	GoogleYahoo	Not checkable here	Read it in Google Postmaster Tools and Yahoo Sender Hub. Google’s target is 0.1%; 0.3% is where enforcement starts.

4 · What to fix, in order

P2
Finish DMARC at p=reject

Quarantine still delivers spoofed mail, just into spam.

Publish at_dmarc.github.com
```
v=DMARC1; p=reject; rua=mailto:dmarc@github.com; fo=1
```
P3
Publish MTA-STS (record and policy file)

Tells sending servers to require TLS to your MX hosts, which prevents downgrade attacks. The TXT record alone does nothing: the policy file must be served over HTTPS at mta-sts.github.com. Start in testing mode, watch TLS-RPT, then switch to enforce.

Publish at_mta-sts.github.com and https://mta-sts.github.com/.well-known/mta-sts.txt
```
TXT  v=STSv1; id=2026100401

mta-sts.txt:
version: STSv1
mode: testing
mx: github-com.mail.protection.outlook.com
max_age: 86400
```
P3
Publish TLS-RPT

You get a report when TLS delivery to your domain fails; this is what notices a downgrade that MTA-STS is meant to prevent. The address must exist.

Publish at_smtp._tls.github.com
```
v=TLSRPTv1; rua=mailto:tls-rpt@github.com
```
P3
Add a BIMI logo record (optional)

DMARC already qualifies. The logo must be SVG Tiny PS, square, served over HTTPS. Yahoo and Fastmail show it from the record alone; Gmail and Apple Mail also need a paid VMC or CMC certificate, and a VMC needs a registered trademark. Skip this unless the certificate is worth it to you.

Publish atdefault._bimi.github.com
```
v=BIMI1; l=https://github.com/.well-known/bimi.svg;
```
P3

Sign the zone with DNSSEC

Protects every record in this report from being swapped in transit. Two steps: enable signing at your DNS host (one switch at Cloudflare and most others), then add the DS record it gives you at your registrar.

Publish atgithub.com

Appendix · Raw DNS answers

Name	Type	Answer
github.com	MX	10 github-com.mail.protection.outlook.com
github.com	A	20.207.73.82
github.com	TXT	v=spf1 ip4:192.30.252.0/22 include:spf.protection.outlook.com include:_netblocks.google.com include:_netblocks2.google.com include:mail.zendesk.com include:_spf.salesforce.com include:servers.mcsv.net include:mktomail.com include:sendgrid.net ip4:62.253.227.114 ip4:166.78.69.169 ip4:166.78.69.170 ip4:166.78.71.131 ~all (+ 23 other TXT records: site-verification tokens and the like, omitted)
_dmarc.github.com	TXT	v=DMARC1; p=quarantine; sp=reject; pct=100; rua=mailto:dmarc@github.com; ruf=mailto:dmarc@github.com; fo=1
<selector>._domainkey.github.com	TXT	google → key published selector1 → CNAME selector1-github-com._domainkey.microsoft.onmicrosoft.com k1 → CNAME dkim.mcsv.net k2 → CNAME dkim2.mcsv.net k3 → CNAME dkim3.mcsv.net s1 → CNAME s1.domainkey.u51742174.wl175.sendgrid.net s2 → CNAME s2.domainkey.u51742174.wl175.sendgrid.net
_mta-sts.github.com	TXT	no record
_smtp._tls.github.com	TXT	no record
default._bimi.github.com	TXT	no record

About this report

The Email Stack reads public DNS for well-known domains and publishes the result as a report, the same one anyone can generate for any domain at /report. It is a point-in-time read: records change, and a domain that scores C today may score differently next month. The "Re-run live" button reads DNS again in your browser.

Scores weigh SPF 20, DKIM 15, DMARC 30, MX 10, MTA-STS 10, TLS-RPT 5, BIMI 5 and DNSSEC 5. Tools are named only when a DNS record names the vendor; a shared DKIM selector counts only when its CNAME target does. Message-level requirements such as alignment and one-click unsubscribe cannot be read from DNS and are marked as such, never guessed. Method: how we detect tools.

Own this domain and see something wrong? DNS is the source; fix the record and the next read will show it. Questions to hello@theemailstack.com.

github.comemail setup

github.com

1 · Authentication and transport

2 · Tools visible in DNS

3 · Sender requirements (Google, Yahoo, Microsoft)

4 · What to fix, in order

Finish DMARC at p=reject

Publish MTA-STS (record and policy file)

Publish TLS-RPT

Add a BIMI logo record (optional)

Sign the zone with DNSSEC

Appendix · Raw DNS answers

About this report