co2online.de

Checked 21 October 2026, 22:10 UTC · via 8.8.8.8
✗Problems found
25 passed 4 warnings 2 failed 2 info

SPF

fail

SPF record published

Found

Record
v=spf1 a mx a:mail.senercon.de a:mail.co2online.de a:mailout.cronon-customer.net ip4:192.166.196.127 include:spf.protection.outlook.com include:_spf.zimpel.de include:one.zoho.eu -all
DNS lookups
11 of 10
Void lookups
0 of 2

Checks

  • ✓ No deprecated ptr mechanism #1
    No ptr mechanism found in SPF record.
  • ✗
    11 DNS lookups, over the limit of 10
    SPF record needs 11 DNS lookups (including nested includes), more than the limit of 10. Receivers will return a permerror; reduce includes or flatten the record.
    #2
  • ✓ 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

pass

p=reject (_dmarc.co2online.de)

Found

Record
v=DMARC1; p=reject; sp=reject; rua=mailto:kontakt@co2online.de
Found at
_dmarc.co2online.de
TagValueMeaning
vDMARC1Version
prejectPolicy
sprejectSubdomain policy
ruamailto:kontakt@co2online.deAggregate report addresses

Checks

  • ✓ Policy: reject #4
    DMARC policy is set to 'reject', which provides the strongest protection against email spoofing.
  • ✓ 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:kontakt@co2online.de
  • ✓ Subdomain policy: reject #20
    Subdomains are covered by policy 'reject'.
  • ✓ Report addresses in own domain #29
    All report addresses are in your own organizational domain.

DKIM

warn

Selectors: k1, selector1

Found

Selectors
k1, selector1
_domainkey
NOERROR
SelectorKeyFlags
k1RSA 1024 bits
selector1RSA 2048 bits

Checks

  • ✓ Keys found: k1, selector1 #7
    DKIM keys found for this domain with selectors: k1, selector1
  • !
    1024-bit DKIM key
    1024-bit RSA keys are the minimum and are considered weak today: k1 (1024 bits). Rotate to a 2048-bit key.
    #23
  • ✓ No problematic flags #24
    No keys in test mode, revoked, or limited to SHA-1.

DNSSEC

warn

Not signed

Found

DNSKEY records
No (0)
DS at parent
No

Checks

  • !
    Not enabled
    DNSSEC is not enabled for this domain. Consider enabling DNSSEC to protect against DNS spoofing attacks.
    #8

MX

warn

1 mail server

Found

PriorityHostRecordsReverse DNS
10co2online-de.mail.protection.outlook.comA 52.101.170.1 A 52.101.170.2 A 52.101.168.0 A 52.101.170.0 AAAA 2a01:111:f403:ca27:: AAAA 2a01:111:f403:ca2d::1 AAAA 2a01:111:f403:ca2d::2 AAAA 2a01:111:f403:ca2d::mail-fr4p281cu03101.inbound.protection.outlook.com ✓ mail-fr6p281cu00202.inbound.protection.outlook.com ✓ mail-beup281cu00100.inbound.protection.outlook.com ✓ mail-fr5p281cu00500.inbound.protection.outlook.com ✓ mail-beup281cu00100.inbound.protection.outlook.com ✓ mail-fr4p281cu03101.inbound.protection.outlook.com ✓ mail-fr6p281cu00202.inbound.protection.outlook.com ✓ mail-fr5p281cu00500.inbound.protection.outlook.com ✓

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 8 MX addresss have a PTR record that resolves back to them.

TLS

warn

no MTA-STS · no TLS-RPT · DANE on 0 of 1 MX hosts

Found

DANE (TLSA records)

MX hostTLSADNSSEC
co2online-de.mail.protection.outlook.comnone-

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
  • i
    Not configured
    TLS-RPT lets senders report TLS delivery problems to you. It is most useful together with MTA-STS or DANE.
    #35
  • i
    Not used
    No MX host publishes TLSA records. DANE lets senders verify your mail server's certificate through DNSSEC; it requires DNSSEC on the MX host's zone.
    #36

BIMI

fail

https://www.co2online.de/co2online/co2online-bimi.svg

Found

Record
v=BIMI1; l=https://www.co2online.de/co2online/co2online-bimi.svg; a=self
Found at
default._bimi.co2online.de
Logo
https://www.co2online.de/co2online/co2online-bimi.svg
Certificate
self

Checks

  • ✗
    Invalid BIMI record
    Mail clients ignore the BIMI record because of: certificate URL "self" must use https://.
    #38
  • ✓ DMARC meets BIMI requirements #39
    DMARC is enforced on all mail, as BIMI requires.