cantorgymnasium.de

Checked 21 October 2026, 22:06 UTC · via 8.8.8.8
✗Problems found
26 passed 7 warnings 1 failed

SPF

pass

SPF record published

Found

Record
v=spf1 a mx -all
DNS lookups
2 of 10
Void lookups
0 of 2

Checks

  • ✓ No deprecated ptr mechanism #1
    No ptr mechanism found in SPF record.
  • ✓ 2 of 10 DNS lookups #2
    SPF record needs 2 DNS lookups (limit is 10).
  • ✓ Ends with -all #3
    SPF record properly uses -all to restrict unauthorized senders.
  • ✓ Record published #6
    SPF record exists for this domain.
  • ✓ Single record #16
    Exactly one SPF record is published.
  • ✓ Valid syntax #25
    All SPF mechanisms and modifiers are valid.
  • ✓ No void lookups #26
    All include/redirect targets exist.
  • ✓ No overly broad IP ranges #27
    All ip4/ip6 ranges are narrow enough.

DMARC

warn

p=quarantine (_dmarc.cantorgymnasium.de)

Found

Record
v=DMARC1; p=quarantine; rua=mailto:mailer@cantor-gymnasium.de
Found at
_dmarc.cantorgymnasium.de
External report address
mailto:mailer@cantor-gymnasium.de (not authorized)
TagValueMeaning
vDMARC1Version
pquarantinePolicy
ruamailto:mailer@cantor-gymnasium.deAggregate report addresses

Checks

  • !
    Policy: quarantine
    DMARC policy is set to 'quarantine'. Consider upgrading to 'reject' for stronger protection once you've verified legitimate emails are passing authentication.
    #4
  • ✓ Record published #5
    DMARC record exists for this domain.
  • ✓ Valid syntax #17
    DMARC record syntax is valid.
  • ✓ Applies to 100% of mail #18
    DMARC policy applies to all failing mail.
  • ✓ Aggregate reports enabled #19
    Aggregate reports are sent to: mailto:mailer@cantor-gymnasium.de
  • ✓ Subdomain policy: quarantine #20
    Subdomains are covered by policy 'quarantine'.
  • !
    Report address not authorized
    These report addresses are in another domain that has not agreed to receive your reports, so receivers will not send them: mailto:mailer@cantor-gymnasium.de (needs cantorgymnasium.de._report._dmarc.cantor-gymnasium.de). Ask the report provider to publish the record, or check the address.
    #29

DKIM

pass

Selectors: dkim

Found

Selectors
dkim
_domainkey
NOERROR
SelectorKeyFlags
dkimRSA 2048 bits

Checks

  • ✓ Keys found: dkim #7
    DKIM keys found for this domain with selectors: dkim
  • ✓ Strong keys #23
    DKIM keys are strong enough: dkim: RSA 2048 bits.
  • ✓ No problematic flags #24
    No keys in test mode, revoked, or limited to SHA-1.

DNSSEC

warn

Signed, but no DS at parent

Found

DNSKEY records
Yes (2)
DS at parent
No
Algorithms
ECDSAP256SHA256 (13)
Key tags
34505, 2371
Signatures valid until
15 December 2026, 17:21 UTC

Checks

  • !
    Signed, but no DS at parent
    The zone is signed (DNSKEY present) but the parent has no DS record, so the chain of trust is incomplete. Publish the DS record at your registrar.
    #8
  • ✓ Signatures valid until 2026-12-15 #21
    DNSKEY signatures are valid until 2026-12-15T17:21:28Z.

MX

warn

1 mail server

Found

PriorityHostRecordsReverse DNS
10mail.cantorgymnasium.deA 152.53.135.72 AAAA 2a0a:4cc0:c0:1f1b::1mail.cantorgymnasium.de ✓ mail.cantorgymnasium.de ✓

Checks

  • ✓ 1 MX record #9
    Found 1 MX records for this domain.
  • ✓ All hosts resolve #10
    All MX records resolve to valid IP addresses.
  • ✓ All hosts have IPv6 #11
    All MX records resolve to IPv6 addresses.
  • !
    Single MX host, no backup
    Only one MX record found. For better email reliability, consider adding at least one backup MX server.
    #12
  • ✓ At most 5 MX records #13
    Found 1 MX records, which is within the recommended range (1-5).
  • ✓ No localhost targets #14
    No MX records pointing to localhost found.
  • ✓ No private IP addresses #15
    No MX records resolving to private IP addresses found.
  • ✓ No CNAME targets #22
    No MX records point to a CNAME.
  • ✓ Reverse DNS confirmed #30
    All 2 MX addresss have a PTR record that resolves back to them.

TLS

fail

no MTA-STS · no TLS-RPT · DANE on 1 of 1 MX hosts

Found

DANE (TLSA records)

MX hostTLSADNSSEC
mail.cantorgymnasium.de3 1 1 eba5e76ad8f5a663… 3 1 1 20ddb5603f0b511a…No

Checks

  • !
    Not configured
    MTA-STS is not configured, so other mail servers fall back to unencrypted delivery when TLS fails or is stripped by an attacker. Publish a _mta-sts TXT record and a policy at https://mta-sts.<domain>/.well-known/mta-sts.txt.
    #32
  • !
    Not configured
    MTA-STS or DANE is used without TLS-RPT, so you get no reports when senders fail to deliver because of TLS problems. Publish _smtp._tls TXT "v=TLSRPTv1; rua=mailto:...".
    #35
  • ✗
    TLSA records not DNSSEC-validated
    These MX hosts publish TLSA records that the resolver could not validate with DNSSEC, so senders ignore them or, if validation fails, may refuse delivery: mail.cantorgymnasium.de.
    #36

BIMI

warn

https://mail.cantorgymnasium.de/bimi.svg

Found

Record
v=BIMI1; l=https://mail.cantorgymnasium.de/bimi.svg; a=;
Found at
default._bimi.cantorgymnasium.de
Logo
https://mail.cantorgymnasium.de/bimi.svg

Checks

  • !
    No certificate (a=)
    The logo is published without a Verified Mark Certificate. Gmail and Apple Mail only show BIMI logos with a VMC or CMC; Yahoo shows it without one.
    #38
  • ✓ DMARC meets BIMI requirements #39
    DMARC is enforced on all mail, as BIMI requires.