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mxcheck

v2.0.0 open-source

Info scanner for e-mail servers checking DNS records, DANE/TLSA, TLS, open ports, blacklists, SMTPSmuggling, and open relay status.

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Summary

mxcheck is an open-source, free command-line scanner that audits an e-mail server's DNS and transport security posture, checking MX, SPFSPFAn email authentication standard that lets a domain owner publish, via DNS, which mail servers are authorized to send on its behalf, so receiving servers can reject spoofed senders., DKIMDKIMAn email authentication standard that lets a sending mail server cryptographically sign outgoing messages so receiving servers can verify the signature was not forged or tampered with in transit., DMARC, MTA-STSSTSAWS Security Token Service, an Amazon Web Services API that issues short-lived credentials for IAM roles, letting cyber tools authenticate to AWS without storing long-term secrets., TLSRPT, BIMI and DANE/TLSA records alongside StartTLS support, open ports, blacklist status and SMTPSMTPThe application-layer protocol used to send email between servers and from clients to servers; cyber tools use it to relay alerts, phishing simulations, or exfiltrated data over standard mail infrastructure. smuggling vulnerability. It runs as a single Go binary against a target domain, with flags to set a DNS server, DKIM selector, disable port scanning or write a TSVTSVA plain-text format storing tabular data with fields separated by tab characters, making it easy for cyber tools to parse and exchange structured records without a CSV parser's quoting complexity. report, which suits mail administrators and security engineers auditing mail infrastructure rather than broad network recon. It sits in the reconnaissance category alongside other DNS and mail-hygiene checkers, focused specifically on the mail-server surface. First committed in 2018 and still active, with 7 contributors and 26 commits in the past year across seven tracked releases, the most recent 136 days ago.

Info scanner for e-mail servers checking DNS records, DANE/TLSA, TLS, open ports, blacklists, SMTPSmuggling, and open relay status.

How mxcheck helps

Which of my e-mail authentication records are missing or misconfigured before a spammer or auditor finds out?

parses SPF, DKIM, DMARC, MTA-STS, TLSRPT and BIMI for the domain and reports each record's presence and content, so gaps in the authentication chain show up directly

Is my mail server exposing a transport-layer weakness right now?

connects to each MX host to check StartTLS support, pulls the TLS certificate details and checks DANE/TLSA records against the host's certificate, flagging mismatches or missing pinning

Is my mail server vulnerable to SMTP smuggling?

actively probes the target server for the smuggling behavior and reports whether the vulnerability is present

Has my domain's mail service ended up on a blacklist?

checks the service against blacklist sources and reports listing status alongside the rest of the scan

Is my server unintentionally relaying mail for anyone who asks?

sends test messages using configurable mailFrom and mailTo addresses, from both external and local perspectives, to check whether the server accepts and forwards mail it shouldn't

Which ports and information leaks on my mail server would a scan from outside reveal?

scans ports 25, 465 and 587 and inspects the server banner and VRFY command response to show what an external prober would learn, with an option to skip the port scan where probing isn't wanted

all 14 features, with the evidence for each →

Languages

Not documented

Features

14 capabilities across 2 capability groups · 6 backed by code, an API document or a real run

Built from mxcheck's releases, docs, README and our own runs. “Seen” marks the month we first spotted a release the vendor didn't date. Group names and tags are our labels.

Compare with peers →

  • mxcheck covers 2 of the 13 network discovery and scanning capabilities we track.

What mxcheck offers you

  • Command-line interface2
Service and version detection 2 features Network discovery and scanning since 2022
TLS certificate inspection shipped Inspects and displays TLS certificate details for MX hosts. 3 releases · first seen Mar 2024

Shared capability: Service and version detection

release

  • Adds TLS certificate detail inspection per MX host. v2.0.0 · Apr 2026 · source · release history
  • Adds TLS certificate details display per MX host 1.9.0 · Mar 2026 · source · release history
  • Adds automatic TLS version checking for the highest version used in STARTTLS and smtps on port 465 v1.6.0-BETA-1 · Mar 2024 · source · release history
Server software identification shipped Identifies the target mail server software by reading and returning the initial line of the SMTP server banner. 1 release · first seen Mar 2022

Shared capability: Service and version detection

release

  • mxcheck now reads the server banner and returns the first line of the response to identify user server software. v1.2.4 · Mar 2022 · source · release history
DNS record enumeration 2 features Network discovery and scanning since 2026
DNS-based MX resolution verified Performs DNS lookups to resolve MX records as the foundation of mail service analysis; requires network connectivity to a DNS resolver. 2 other sources · first seen Aug 2026

Shared capability: DNS record enumeration

we ran it

  • The tool failed immediately with a network error — it attempted a UDP DNS lookup against 8.8.8.8:53 but the network was unreachable. No findings were produced. Aug 2026 · the full run

example

  • Scan using specific DNS server ./mxcheck -s 2600.com -d 8.8.8.8
TLSRPT record checking shipped Looks up and parses TLSRPT records to provide visibility into mail transport security reporting. 2 releases · first seen Mar 2026

Shared capability: DNS record enumeration

release

  • Adds TLSRPT record lookup and parsing for mail transport security reporting visibility. v2.0.0 · Apr 2026 · source · release history
  • Adds new TLSRPT record checking capability 1.9.0 · Mar 2026 · source · release history
Other / not yet classified 10 features Features we have not matched to a capability yet. A suggested match is marked.
Blacklist check verified Checks whether the target mail service appears on known blacklists. 1 release · 4 other sources · first seen Oct 2022

release

  • Prefixes blacklist results with _Blacklist_ in the output file v1.5.1 · May 2023 · source · release history

command line

  • --blacklist — Check if the service is on blacklists v1.4.0-BETA · Oct 2022 · command-line history

example

  • Check open relay with local addresses ./mxcheck -s example.com -f info@example.com -t boss@example.com
  • Check open relay with external addresses ./mxcheck -s example.com -f info@baz.com -t boss@foo.org
  • Scan with blacklist and SMTPSmuggling checks ./mxcheck -s 2600.com -n -f info@baz.com -t boss@foo.org -w -S default -b -g
Verbose output with timestamps verified Includes timestamps in tool output when verbose mode is enabled. 2 releases · 2 other sources · first seen Mar 2026

release

command line

we ran it

  • The tool printed a timestamped error immediately: it could not reach the DNS resolver at 8.8.8.8:53 because the network was unreachable. No MX analysis was completed. Aug 2026 · the full run
SMTP smuggling detection verified Tests the target mail service for the SMTP smuggling vulnerability. 1 release · 3 other sources · first seen Nov 2025

Also counts toward: Command-line interface

release

  • New -g flag enables active checks for the SMTP Smuggling vulnerability against target mail servers. v1.8.0 · Nov 2025 · source · release history

command line

example

  • Test a mail server for SMTP Smuggling susceptibility as part of a mail-infrastructure audit. mxcheck -g -target mail.example.com v1.8.0 · Nov 2025 · source
  • Scan with blacklist and SMTPSmuggling checks ./mxcheck -s 2600.com -n -f info@baz.com -t boss@foo.org -w -S default -b -g
DMARC record parsing shipped suggested Parses full DMARC records to analyze policy and alignment for mail domain authentication. 2 releases · 1 other source · first seen Mar 2026

Suggested capability: DNS record enumeration. This is our guess, not confirmed.

release

example

  • Scan with DKIM selector and TSV report ./mxcheck -s 2600.com -n -f info@baz.com -t boss@foo.org -w -S default
SMTP port scanning verified suggested Scans SMTP ports as part of mail service analysis, with an option to disable this behaviour. 1 release · 2 other sources · first seen Jun 2025

Suggested capability: Attack surface inventory. This is our guess, not confirmed.

Also counts toward: Command-line interface

release

  • Adds -p flag to skip the port scan phase, allowing faster or quieter MX checks when port scanning is unwanted. v1.7.0 · Jun 2025 · source · release history

command line

example

  • Run an MX check without triggering a port scan — useful in environments where outbound port probing is restricted or noisy. mxcheck -p <domain> v1.7.0 · Jun 2025 · source
BIMI record checking shipped suggested Checks and detects BIMI records to verify brand indicator information for displayed mail clients. 2 releases · first seen Mar 2026

Suggested capability: DNS record enumeration. This is our guess, not confirmed.

release

Open relay detection shipped Detects whether the target mail server allows unauthorized third-party email forwarding by testing connections with local and external addresses. 2 other sources

example

  • Check open relay with local addresses ./mxcheck -s example.com -f info@example.com -t boss@example.com
  • Check open relay with external addresses ./mxcheck -s example.com -f info@baz.com -t boss@foo.org
DANE/TLSA record checking shipped Validates DNS-based authentication of named entities by checking DANE/TLSA records per MX host. 1 release · first seen Apr 2026

release

  • Adds DANE/TLSA record checking per MX host to validate DNS-based authentication of named entities. v2.0.0 · Apr 2026 · source · release history
Expanded ASN network attribution shipped Retrieves and exposes additional ASN fields from IP lookups for richer network attribution of MX hosts. 1 release · first seen Apr 2026

release

  • Exposes additional ASN fields from iptoasn lookups for richer MX host network attribution. v2.0.0 · Apr 2026 · source · release history
Update check verified Checks whether a newer version of mxcheck is available. 1 other source · first seen May 2023

command line

Lines in monospace are the tool's own words: help text parsed from its source, or an endpoint from its API document. Under release, a line is our summary of a dated release. Under docs, it is quoted from the tool's own documentation or website. Each links back to the source it came from.

Score card

  1. Shipping velocity releases a month, last 12 months
  2. Documentation quality release-notes rubric, 0–100
  3. Breaking-change discipline how rarely a release breaks users, and notice given
  4. Maintenance risk quiet time against its own cadence, maintainers
  5. Innovation & surface new capabilities, API and MCP surface
  6. Community health
  7. Contributor trend distinct committers, this year against last
  8. Maintainer concentration bus factor now against a year ago
  9. Issue backlog trend issues closed per issue opened, 12 months
  10. Responsiveness median time to a maintainer’s first reply

Nine scores for mxcheck, each built from the releases, notes and API history this site tracks — and, on Researcher and Business, where it stands among every measured tool in its category and how that has moved.

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Each score is 0–100 on a published rubric, derived from data this site already shows. A dimension we cannot measure says so — it is never scored 0 and never enters a rank.

How this is scored
  • Shipping velocity — releases a month over the last 12 months, on a log scale where 16 a month scores 100. Needs 3 releases in the window.
  • Documentation quality — the release-notes rubric published on the analytics page, unchanged.
  • Breaking-change discipline — the share of releases carrying a breaking change (none scores 100, half or more scores 0). Only projects that label breaking changes are measured: a clean record cannot be told from an unlabelled one.
  • Maintenance risk — quiet time measured against the tool's own release cadence (quiet longer than 90 days and three typical gaps scores 0), plus the number of active maintainers and whether contributors are growing, where known. Higher is lower risk.
  • Innovation & surface — new capabilities in the feature ledger this year, API and MCP operations added, and the share of commits that are features: the mean of whichever we hold.
  • Community health (open-source tools only) — each is a direction, not a size: contributors this year against last, the bus factor now against a year ago, and issues closed per issue opened, where steady scores 50, doubled 100 and halved 0; plus the median time to a maintainer's first reply (an hour scores about 100, a month or more 0). A commercial card has no repository and carries none of the four.
  • Documented delivery (commercial tools) — when a vendor's documented new capabilities have slowed against its own baseline, that counts against the overall standing as heavily as two low dimensions. Steady delivery, or too little history to judge, leaves the standing alone; it is never a sixth score.
  • Open-source tools are scored on repository signals; commercial tools on their published changelog. Ranks compare tools within one category and one profile and need at least five measured peers; the overall standing needs three ranked dimensions. Best-in-breed or consolidator is a shape, not a quality, and is never scored.

Release-note detail over time

See how much detail mxcheck puts in its release notes, quarter by quarter, and compare it with tracked tools in the same category. This history uses up to ten retained, reviewed notes per tool; sparse or blank older quarters may reflect that limit.

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Releases

Show

7 entries

  1. April 20261
  3. March 20261
  5. November 20251
  7. June 20251
  9. March 20241
  11. May 20231
  13. March 20221
    Show

    7 entries

    1. v2.0.0 Apr 7, 2026 · release notes

      mxcheck v2.0.0 adds TLSRPT, BIMI, full DMARC parsing, DANE/TLSA checks, TLS cert details, expanded ASNASNAutonomous System Number — a globally unique identifier assigned by regional internet registries to a network operator, letting routing protocols distinguish which organization controls a block of IP addresses. fields, and a --verbose flag.

      └──▷ GET THIS VERSION 
      $ git clone --branch v2.0.0 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v2.0.0
      └──▷ TRY IT
      Get full structured outputstructured outputForcing a model's response to match a given format or JSON schema, so software can parse it reliably instead of hoping the text is well formed. including DMARC, BIMI, TLSRPT, DANE/TLSA, TLS cert, and expanded ASN details for a domain under investigation.
      $ mxcheck --verbose example.com
      • Adds TLSRPT record lookup and parsing for mail transport security reporting visibility.
      • Adds BIMI record detection for brand indicator verification checks.
      • Adds full DMARC record parsing beyond basic presence detection.
      • Adds TLS certificate detail inspection per MX host.
      • Adds DANE/TLSA record checking per MX host to validate DNS-based authentication of named entities.
      +2 more show less
      • Exposes additional ASN fields from iptoasn lookups for richer MX host network attribution.
      • Adds --verbose flag for structured, detailed CLI output.

      7 details in Everything

    2. 1.9.0 Mar 1, 2026 · release notes

      mxcheck v1.9.0 adds TLSRPT and BIMI record checks with per-MX TLS cert details

      └──▷ GET THIS VERSION 
      $ git clone --branch 1.9.0 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout 1.9.0
      • Adds --verbose flag to the CLI for detailed output
      • Adds new TLSRPT record checking capability
      • Adds new BIMI record checking capability
      • Adds full DMARC parsing support
      • Adds TLS certificate details display per MX host

      5 details in Everything

    3. v1.8.0 Nov 24, 2025 · release notes

      mxcheck v1.8.0 adds active SMTPSMTPThe application-layer protocol used to send email between servers and from clients to servers; cyber tools use it to relay alerts, phishing simulations, or exfiltrated data over standard mail infrastructure. Smuggling vulnerability detection via new -g flag.

      └──▷ GET THIS VERSION 
      $ git clone --branch v1.8.0 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v1.8.0
      └──▷ TRY IT
      Test a mail server for SMTP Smuggling susceptibility as part of a mail-infrastructure audit.
      $ mxcheck -g -target mail.example.com
    4. v1.7.0 Jun 3, 2025 · release notes

      mxcheck v1.7.0 adds a -p flag to disable port scanning on demand.

      └──▷ GET THIS VERSION 
      $ git clone --branch v1.7.0 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v1.7.0
      └──▷ TRY IT
      Run an MX check without triggering a port scan — useful in environments where outbound port probing is restricted or noisy.
      $ mxcheck -p <domain>
      • Adds -p flag to skip the port scan phase, allowing faster or quieter MX checks when port scanning is unwanted.

      1 detail in Everything

    5. v1.6.0-BETA-1 Prerelease Mar 15, 2024 · release notes

      mxcheck v1.6.0-BETA-1 adds automatic TLS version checking for STARTTLSSTARTTLSA protocol command that upgrades a plaintext connection to an encrypted TLS session without changing ports, used in SMTP, IMAP, and LDAP so tools can negotiate encryption opportunistically on standard service ports. and SMTPS

      └──▷ GET THIS VERSION 
      $ git clone --branch v1.6.0-BETA-1 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v1.6.0-BETA-1
    6. v1.5.1 May 15, 2023 · release notes

      mxcheck v1.5.1 adds DMARC check and blacklist prefix for output parsing

      └──▷ GET THIS VERSION 
      $ git clone --branch v1.5.1 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v1.5.1
      • Prefixes blacklist results with _Blacklist_ in the output file

      1 detail in Everything

    7. v1.2.4 Mar 20, 2022 · release notes

      mxcheck v1.2.4 adds server banner extraction via the Serverident feature

      └──▷ GET THIS VERSION 
      $ git clone --branch v1.2.4 https://github.com/steffenfritz/mxcheck.git
# already have the repo? check out this version:
$ git checkout v1.2.4
      • mxcheck now reads the server banner and returns the first line of the response to identify user server software.

      1 detail in Everything

    Project health

    Issue, contributor and maintainer activity in steffenfritz/mxcheck, 2023-10 – 2026-09, as of 2026-09-25. Twelve-month figures first; the trend lines run the whole window.

    1. Contributors 2 −1 vs prior 12 months
    2. Maintainers 2 +1 joined · −1 left, last 12 months
    3. Bus factor 1 committers behind half the commits
    4. Community-filed 0% of issues opened, last 12 months
    5. Median time to close < 1 day first maintainer reply 0.5 hours
    6. Open backlog 0 of 27 issues ever filed
    1. Issues opened / month 0 · 0 communitymaintainers
    2. Open backlog 0
    3. Contributors / month 0
    4. Commits / month 0
    5. Stars 146
    Issue themes, last 12 months
    • features 50%
    • other 50%

    Counts from the project's public repository and git history; no individuals are identified. Maintainers are the committers covering 80% of the last year's commits. how we measure this

    Libraries its release ships

    What its latest release locks, checked against known advisories.

    None of its release's images build from a lockfile we can read.

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