gcdn.co
Poor, with 5 things to fix
gcdn.co scored 50/100 (grade D). The main issues are no DMARC record and no DKIM key found for the common selectors, plus 5 more. Detected senders: Microsoft 365.
Checked 2026-10-04 02:11 UTC · fresh check
Diagnosis notes
- Warning: DNS lookup budget exhausted
This diagnosis stopped sending DNS queries after 150 queries. Checks that needed more lookups report their remaining results as unknown; the domain's records may be unusually large or slow to answer.
Publish a DMARC record
Starts DMARC in monitoring mode (p=none), so you can see who sends as gcdn.co before enforcing a policy. Move to quarantine once the reports show only your own services.
_dmarc.gcdn.co
Some DNS providers want just “_dmarc” here.
v=DMARC1; p=none; adkim=r; aspf=r
How to apply it
- Sign in where your domain’s DNS is managed. This is often where you bought the domain, such as Cloudflare, GoDaddy or Namecheap.
- Add a new TXT record with the name and value above.
- Save, then come back and re-check. DNS changes can take up to a few hours to show.
All checks
MXCan servers find your inbox?Only one MX hostInfo
- Info: Only one MX host
All mail for gcdn.co goes to mail.gcdn.co. Most hosted providers make that one name highly available; if you run your own server, consider a backup MX.
SPFWho may send as you?Included domain has no SPF recordNeeds attention
- Warning: Included domain has no SPF record
The SPF record refers to net2.gc.onl (include or redirect), which publishes no SPF record. Receivers treat that as a permanent error. Check the provider's current include domain or remove it.
- Info: SPF ends in softfail (~all)
"~all" is common and works well with DMARC. "-all" is stricter; switch when you are sure every sender is listed.
DKIMAre your emails signed?No DKIM key found for the common selectorsNeeds attention
- Warning: No DKIM key found for the common selectors
None of the 47 selectors probed under gcdn.co publish a DKIM key. DNS cannot list selectors, so a key under a custom selector may exist: find the s= value in the DKIM-Signature header of a message you sent and check that selector. If DKIM is not set up, enable it at each service that sends mail for gcdn.co.
- Warning: Some DKIM lookups failed
27 of 47 selector lookups under gcdn.co returned TIMEOUT, so whether those selectors hold a key is unknown. Try again later; if it persists, check the domain's nameservers.
DMARCWhat happens to fakes?No DMARC recordFailing
- Fail: No DMARC record
There is no v=DMARC1 TXT record at _dmarc.gcdn.co. Without DMARC, receivers have no policy for mail that fails SPF and DKIM, and Gmail and Yahoo require one for bulk senders. Start with p=none and a rua address to collect reports.
How to fix this
AlignmentDoes it match your From?SPF alignment is unknownInfo
- Info: SPF alignment is unknown
The SPF record of gcdn.co can pass for some senders (those matched before the failing part), but another evaluation path ends in a permanent error (spf.include.missing). Senders that reach that path fail SPF, so whether your mail aligns through SPF is unknown. Fix the error so every path evaluates.
BIMICan inboxes show your logo?Could not look up the BIMI recordNeeds attention
- Warning: Could not look up the BIMI record
The TXT query for default._bimi.gcdn.co returned TIMEOUT, so BIMI status is unknown. Try again later.
MTA-STSIs mail to you encrypted?Could not look up the MTA-STS recordNeeds attention
- Warning: Could not look up the MTA-STS record
The TXT query for _mta-sts.gcdn.co returned TIMEOUT, so MTA-STS status is unknown. Try again later.
TLS-RPTWill you hear about failures?No TLS-RPT recordInfo
- Info: No TLS-RPT record
No TLS reporting record at _smtp._tls.gcdn.co. TLS-RPT (RFC 8460) tells senders where to send daily reports about failed encrypted deliveries to you.
How to fix this
Other fixes
Enable DKIM for Microsoft 365instruction
Microsoft 365 generates the DKIM key for each account, so the exact record must come from Microsoft 365. Without DKIM, mail it sends for gcdn.co cannot pass DMARC through DKIM.
Applies to: selector1._domainkey.gcdn.co
- In Microsoft 365, enable DKIM signing for gcdn.co: tenant-specific: copy Selector1CNAME/Selector2CNAME from Microsoft 365 Defender > Email authentication > DKIM. Publish exactly the record Microsoft 365 shows (TXT or CNAME) at the host name it gives, then turn signing on. Instructions: https://learn.microsoft.com/microsoft-365/security/office-365-security/email-authentication-dkim-configure
Enable DKIM for Microsoft 365instruction
Microsoft 365 generates the DKIM key for each account, so the exact record must come from Microsoft 365. Without DKIM, mail it sends for gcdn.co cannot pass DMARC through DKIM.
Applies to: selector2._domainkey.gcdn.co
- In Microsoft 365, enable DKIM signing for gcdn.co: tenant-specific: copy Selector1CNAME/Selector2CNAME from Microsoft 365 Defender > Email authentication > DKIM. Publish exactly the record Microsoft 365 shows (TXT or CNAME) at the host name it gives, then turn signing on. Instructions: https://learn.microsoft.com/microsoft-365/security/office-365-security/email-authentication-dkim-configure
Set up a TLS report addressinstruction
Sending servers will report TLS failures when delivering to gcdn.co, 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.gcdn.co
- Pick an address that will receive TLS reports: a mailbox you read (for example tls-reports@gcdn.co, created first) or a TLS reporting service. 2. Publish a TXT record at _smtp._tls.gcdn.co with the value v=TLSRPTv1; rua=mailto:<that address>.