Identity
0
D
slack.com
Posture Score: 61/100
Scanned May 10, 2026 at 5:09 PM UTC
Score History
Attack Surface
91
Reputation
92
Identity Findings
Invalid DKIM syntax for selector 'default'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'selector1'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'selector2'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'google'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'dkim'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'mail'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'k1'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 's1'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 's2'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'mandrill'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'amazonses'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'cm'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
Invalid DKIM syntax for selector 'smtp'
The DKIM record is missing the required p= (public key) tag.
💡 Publish a valid DKIM record with the p= tag containing the public key.
No MTA-STS record found
Without MTA-STS, mail transport encryption cannot be enforced and is vulnerable to downgrade attacks.
💡 Publish a _mta-sts TXT record and host a policy file at https://mta-sts.slack.com/.well-known/mta-sts.txt
STARTTLS without MTA-STS or DANE protection
STARTTLS alone is vulnerable to downgrade attacks. Neither MTA-STS nor DANE is configured to enforce encryption.
💡 Deploy MTA-STS and/or DANE to protect against STARTTLS stripping attacks.
No TLS-RPT record found
Without TLS-RPT, you will not receive reports about TLS negotiation failures.
💡 Publish a _smtp._tls TXT record (e.g. "v=TLSRPTv1; rua=mailto:tls-reports@slack.com").
Shared IP 173.194.76.26 used by multiple MX servers
The IP 173.194.76.26 is shared across 2 MX hostnames, reducing redundancy.
💡 Use unique IP addresses for each MX server for better redundancy.
Shared IP 142.250.102.27 used by multiple MX servers
The IP 142.250.102.27 is shared across 2 MX hostnames, reducing redundancy.
💡 Use unique IP addresses for each MX server for better redundancy.
Slow DNS response from ns-166.awsdns-20.com: 2068.5ms
The nameserver ns-166.awsdns-20.com responded in 2068.5ms, exceeding the 500ms threshold.
💡 Investigate network latency or performance issues on ns-166.awsdns-20.com.
Very low TTL on MX records: 19s
5 MX records have a TTL of 19s or less (below 300s).
💡 Increase the TTL to at least 300 seconds unless frequent changes are expected.
Very low TTL on DMARC record: 259s
The DMARC record has a TTL of 259s or less (below 300s).
💡 Increase the TTL to at least 300 seconds unless frequent changes are expected.
SPF record is valid
The SPF record is properly configured with valid syntax and within lookup limits.
SPF record length OK (91 bytes)
SPF record is within safe DNS packet size limits.
DKIM cryptographic configuration is compliant
No RFC 8301 compliance issues detected in DKIM key configuration.
All external report destinations authorized
External DMARC report destinations have valid authorization records per RFC 7489 §7.1.
Subdomains protected (sp=reject)
DMARC subdomain policy enforces quarantine or reject on unauthenticated subdomain mail.
5 MX records with 4 unique IPs
Multiple MX records provide mail delivery redundancy.
ARC support likely available
MX server software appears to support ARC headers for authentication preservation.
Meets bulk sender authentication requirements
Domain has SPF, DKIM, and DMARC — meeting Google/Yahoo 2024 bulk sender requirements for email authentication.
SMTP security checks passed
No open relay, VRFY/EXPN, or banner disclosure issues detected.
SMTP RFC 5321 compliance checks passed
The mail server accepts postmaster@ and abuse@ and uses a valid FQDN in EHLO.
IPv6 readiness is good
IPv6 records are present and properly configured.
NS delegation is properly configured
All nameservers are responsive, consistent, and properly secured.
DKIM2 not detected
No DKIM key record with v=2 was found across common selectors. DKIM2 is an emerging standard and not yet widely deployed.
DMARC alignment: adkim=r, aspf=r
DKIM alignment is relaxed, SPF alignment is relaxed.
DMARC failure reporting: fo=1:d:s
Failure reporting option: 1:d:s
DMARCbis np tag absent
The DMARC record does not include the np (non-existent subdomain policy) tag. Consider adding np=reject to protect non-existent subdomains under DMARCbis.
Deprecated DMARCbis tags found: pct
The DMARC record contains tags deprecated in DMARCbis: pct. Consider removing these for forward compatibility.
DMARCbis psd tag absent
The DMARC record does not include the psd (public suffix domain) indicator. Consider adding psd=n to explicitly identify this as an organizational domain.
Shared/free email hosting detected: aspmx.l.google.com
The MX record points to a known shared or free email hosting provider.
Shared/free email hosting detected: alt1.aspmx.l.google.com
The MX record points to a known shared or free email hosting provider.
Shared/free email hosting detected: alt2.aspmx.l.google.com
The MX record points to a known shared or free email hosting provider.
REQUIRETLS not advertised
The primary MX does not advertise REQUIRETLS (RFC 8689). This is an emerging standard — MTA-STS and DANE provide adequate TLS enforcement for most deployments.
No DANE/TLSA records found
DANE is not configured for any MX server. This is optional but provides strong certificate binding.
No BIMI record found
BIMI is not configured. Your brand logo will not display in supporting email clients.
Open mail ports on aspmx.l.google.com
Detected open mail-related ports: 25
RFC 8058 one-click unsubscribe assessment
No DKIM signing detected. RFC 8058 one-click unsubscribe requires DKIM-signed List-Unsubscribe headers.
MX IP network diversity
MX IPs span 3 different /16 networks, providing good diversity.
SOA record parameters
Serial: 1, Refresh: 7200s, Retry: 900s, Expire: 1209600s, Min TTL: 300s
Authorized certificate authorities
CAA records restrict certificate issuance to: digicert.com; account=455b15ed272bed097725c6ea50e89921fc57379c5338a29305c05771df65fff1, letsencrypt.org; accounturi=https://acme-v02.api.letsencrypt.org/acme/acct/1532134906
Attack Surface Findings
DNS ANY query returns 32 record(s)
The DNS server responds to ANY queries with 32 record(s), creating significant DNS amplification risk.
💡 Configure the DNS server to refuse or minimize ANY query responses per RFC 8482.
No NSEC/NSEC3 records found
Neither NSEC nor NSEC3 records were found. Authenticated denial of existence is not configured.
💡 Configure NSEC3 records for authenticated denial of existence while preventing zone enumeration.
Domain enumerability: low
The domain has low enumerability. Proper NSEC3 configuration and limited CT exposure reduce the attack surface.
No subdomain takeover risks detected
All checked subdomains have valid, responsive targets.
All MX records resolve correctly
No dangling MX records detected — all MX hostnames resolve to valid IP addresses.
Explicit MX records present
The domain has explicit MX records — no implicit A-record fallback delivery.
No internal information leakage detected
No non-routable IP addresses or internal references were found in public DNS records.
3 subdomain(s) discovered for slack.com
Subdomains were enumerated via Certificate Transparency logs, DNS wordlist brute-forcing, and DNS record analysis.
0 certificate(s) found in CT logs
Certificate Transparency logs contain 0 certificate(s) for slack.com and its subdomains. Each certificate reveals subdomain names.
Wildcard DNS record detected
A wildcard DNS record exists for *.slack.com, resolving to 52.211.94.64, 34.248.150.55, 52.50.161.139, 63.34.91.196. Wildcard records make subdomain brute-forcing less effective but may mask misconfigurations.
Microsoft Autodiscover endpoint detected
The Autodiscover endpoint at autodiscover.slack.com responded with HTTP 404.
DNSSEC is enabled
DNSKEY and/or DS records are present, indicating DNSSEC is configured.
Reputation Findings
SMTP banner mismatch: mx.google.com
The SMTP banner identifies as 'mx.google.com' but the MX hostname is 'aspmx.l.google.com' and PTR resolves to 'dj-in-f26.1e100.net'. Microsoft and other receivers flag this mismatch as suspicious infrastructure.
💡 Configure the SMTP server banner to match the MX hostname or PTR record (aspmx.l.google.com).
HSTS enabled with preload on slack.com
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
HSTS enabled with preload on webmail.slack.com
Strict-Transport-Security: max-age=31536000; includeSubDomains; preload
security.txt present
Found security.txt at https://slack.com/.well-known/security.txt.
TLS certificate valid for 53 days
Certificate for slack.com expires on 2026-07-03.
Certificate issued by R13
The certificate for slack.com is issued by a third-party CA.
Signature algorithm: rsa-sha256
The certificate for slack.com uses an acceptable signature algorithm.
RSA key: 2048 bits
The certificate for slack.com uses an adequate RSA key of 2048 bits.
SCTs present in certificate
The certificate for slack.com contains Signed Certificate Timestamps.
No weak ciphers detected
No known weak cipher suites detected on slack.com.
Domain valid for 527 days
Domain slack.com expires on 2027-10-20.
Domain transfer and delete locks enabled
Domain slack.com has clientTransferProhibited and clientDeleteProhibited locks.
TLD has good reputation
The .com TLD is not on known abuse watchlists.
DMARC reporting destinations look legitimate
DMARC rua/ruf addresses do not point to known URL shortener services.
MX records point to stable infrastructure
No MX records point to known dynamic DNS service domains.
Strong TLS configuration on primary MX
Primary MX (aspmx.l.google.com) uses TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 including Forward Secrecy.
Google Safe Browsing DNS check — no flag detected
DNS-based Safe Browsing lookup returned no results. Full verification requires the Google Safe Browsing API key.
Abuse contact lookup failed
Could not query abuse contact information.
PhishTank — API key required
PhishTank phishing database check requires an API key.
Sender Score — API key required
Sender Score reputation check requires an API key.
Cisco Talos — API key required
Cisco Talos IP reputation check requires an API key.
WHOIS registration data
Registrar: MarkMonitor Inc. | Created: 1992-10-21 | Expires: 2027-10-20 | Updated: 2025-09-18
WHOIS privacy protection not detected
Domain slack.com does not appear to have WHOIS privacy protection. Registrant details may be publicly visible.
Typosquat detected: slac.com (has MX!), salck.com (has MX!), slcak.com (has MX!), alack.com (has MX!), zlack.com (has MX!)
22 registered lookalike domain(s) that could be used for phishing against your brand. Showing top 5 of 22. Domains with MX records can send and receive email, making them high-risk phishing vectors.
Dependency Chains
DMARC Authentication Chain (SPF)
DMARC uses SPF to verify that emails come from authorized servers
SPF Record
SPF record found and configured
→
DMARC Policy
DMARC policy: reject
DMARC Authentication Chain (DKIM)
DMARC uses DKIM to verify that emails have not been tampered with
DKIM Signature
DKIM signature configured
→
DMARC Policy
DMARC policy: reject
Mail Server Identity: aspmx.l.google.com
PTR record proves mail server legitimacy
MX: aspmx.l.google.com
Mail server at 74.125.193.27
→
PTR Record
Reverse DNS: ig-in-f27.1e100.net
Mail Server Identity: alt1.aspmx.l.google.com
PTR record proves mail server legitimacy
MX: alt1.aspmx.l.google.com
Mail server at 173.194.76.26
→
PTR Record
Reverse DNS: ws-in-f26.1e100.net
Mail Server Identity: alt2.aspmx.l.google.com
PTR record proves mail server legitimacy
MX: alt2.aspmx.l.google.com
Mail server at 142.250.102.27
→
PTR Record
Reverse DNS: rb-in-f27.1e100.net
Mail Server Identity: aspmx2.googlemail.com
PTR record proves mail server legitimacy
MX: aspmx2.googlemail.com
Mail server at 173.194.76.26
→
PTR Record
Reverse DNS: ws-in-f26.1e100.net
Mail Server Identity: aspmx3.googlemail.com
PTR record proves mail server legitimacy
MX: aspmx3.googlemail.com
Mail server at 142.250.102.27
→
PTR Record
Reverse DNS: rb-in-f27.1e100.net
Mail Server Reputation: aspmx.l.google.com
RBL check ensures server is not blacklisted
MX: aspmx.l.google.com
Mail server at 74.125.193.27
→
RBL Status
Not blacklisted
Mail Server Reputation: alt1.aspmx.l.google.com
RBL check ensures server is not blacklisted
MX: alt1.aspmx.l.google.com
Mail server at 173.194.76.26
→
RBL Status
Not blacklisted
Mail Server Reputation: alt2.aspmx.l.google.com
RBL check ensures server is not blacklisted
MX: alt2.aspmx.l.google.com
Mail server at 142.250.102.27
→
RBL Status
Not blacklisted
Mail Server Reputation: aspmx2.googlemail.com
RBL check ensures server is not blacklisted
MX: aspmx2.googlemail.com
Mail server at 173.194.76.26
→
RBL Status
Not blacklisted
Mail Server Reputation: aspmx3.googlemail.com
RBL check ensures server is not blacklisted
MX: aspmx3.googlemail.com
Mail server at 142.250.102.27
→
RBL Status
Not blacklisted
Enforced Encryption Chain
MTA-STS enforces TLS encryption to prevent man-in-the-middle attacks
TLS Support
Mail servers support TLS encryption
→
MTA-STS Policy
MTA-STS not configured
⚠️ MTA-STS policy is missing. Even with TLS support, you lack the enforcement layer that prevents attackers from stripping encryption (downgrade attacks).
Brand Identity Chain
BIMI displays your logo in email clients, but requires DMARC enforcement
DMARC Enforcement
DMARC policy: reject
→
BIMI Record
Brand logo configured
TLS Monitoring Chain
TLS-RPT provides reports about TLS connection failures
TLS Support
Mail servers support TLS encryption
→
TLS-RPT Reporting
TLS failure reporting configured
Security Checks
MX Records
✓
SPF Record
✓
DKIM Record
✓
DMARC Policy
✓
BIMI Record
✓
CAA Records
✓
DNSSEC
✓
MTA-STS
✗
TLS-RPT
✓
Embed Badge
Display your domain's security grade on your website or README:
<img src="https://scan.ractermx.com/badge/slack.com.svg" alt="Email Security Grade">
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