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Install SMTP Test Tool using WinGet - wingetCollections
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SMTP Test Tool StruisICT

diagnostic email imap pop3 rustls smtp tls
Use this command to install SMTP Test Tool with WinGet:
winget install --id=StruisICT.SmtpTestTool -e

SMTP Test Tool is a comprehensive diagnostic utility designed to verify SMTP, IMAP, and POP3 connectivity. It helps IT teams troubleshoot email server issues, including SSL/TLS configuration and authentication paths, and translates complex bounce codes into actionable insights.

Key Features:

  • Cross-Platform Support: Runs on multiple operating systems with a single binary download.
  • Integrated CLI and GUI: Offers both command-line interface and graphical user interface for versatile use cases.
  • Multi-Language Support: Available in over 36 languages to accommodate diverse global teams.
  • DNS Audit Capability: Automatically checks MX, SPF, DMARC, and DKIM records to identify configuration issues.
  • OAuth2 Integration: Supports secure authentication via OAuth2 for Microsoft 365 environments.
  • Secure Credential Management: Stores credentials securely using the Windows Credential Manager.

Target Audience and Benefits: Ideal for IT administrators, DevOps engineers, and email server professionals. This tool streamlines troubleshooting by quickly diagnosing issues and providing clear remediation steps, saving time and reducing downtime associated with email server problems.

The application is available via Winget, making deployment straightforward through the winget command line.

README

smtp-test-tool

CI Latest release License: MIT OR Apache-2.0 MSRV

> Cross-platform SMTP / IMAP / POP3 connectivity tester with > IT-actionable diagnostics. CLI and GUI in one single static binary > per OS, no external runtime, no OpenSSL on the host.

When your mail flow breaks at 09:00 on a Monday, this is the tool you hand to your IT department alongside an exact reproduction of the error the server returned — not "it doesn't work".

Screenshots

The GUI follows the OS appearance, with a manual auto / dark / light override on the Advanced tab. Both palettes meet WCAG 2.2 Level AAA contrast on the elements where colour carries information.

DarkLight
Dark themeLight theme

Non-Latin locales pick up an OS-installed font automatically (see Languages for the discovery story). Example renders:

Chinese (zh)Japanese (ja)Korean (see ko.toml)
zhjaOS: Malgun Gothic
Arabic (ar)Persian (fa)Hebrew (he)
Versions
0.2.1
Website
github.com
License
Last updated
7/29/2026
Download latest version
Loading...
arfahe
Hindi (hi)Bengali (bn)Thai (th)
hibnth
Tamil (ta)Telugu (te)
tate

Languages

The GUI, the CLI prompts, and every diagnostic hint can be displayed in any of the currently-shipped locales. The application auto- detects the OS locale on startup and applies it if a translation exists, otherwise falls back to English. The Advanced tab carries a language picker limited to your OS locale + English — deliberately two options at most, so the UI does not grow with the translation set.

Shipped in v0.1.6 — 36 languages (11 non-Latin scripts):

CodeNative nameStatus
enEnglishbase, hand-maintained
nlNederlandsnative quality
arالعربيةmachine-translated, native review welcome (RTL: needs system Arabic font)
bgБългарскиmachine-translated, native review welcome
bnবাংলাmachine-translated, native review welcome (needs system Indic font)
csČeštinamachine-translated, native review welcome
daDanskmachine-translated, native review welcome
deDeutschmachine-translated, native review welcome
elΕλληνικάmachine-translated, native review welcome
esEspañolmachine-translated, native review welcome
faفارسیmachine-translated, native review welcome (RTL: needs system Arabic font)
fiSuomimachine-translated, native review welcome
frFrançaismachine-translated, native review welcome
heעבריתmachine-translated, native review welcome (RTL: needs system Hebrew font)
hiहिन्दीmachine-translated, native review welcome (needs system Indic font)
hrHrvatskimachine-translated, native review welcome
huMagyarmachine-translated, native review welcome
idBahasa Indonesiamachine-translated, native review welcome
itItalianomachine-translated, native review welcome
ja日本語machine-translated, native review welcome (needs system CJK font)
ko한국어machine-translated, native review welcome (needs system CJK font)
noNorskmachine-translated, native review welcome
plPolskimachine-translated, native review welcome
ptPortuguêsmachine-translated, native review welcome
roRomânămachine-translated, native review welcome
ruРусскийmachine-translated, native review welcome
skSlovenčinamachine-translated, native review welcome
srSrpskimachine-translated, native review welcome
svSvenskamachine-translated, native review welcome
taதமிழ்machine-translated, native review welcome (needs system Indic font)
teతెలుగుmachine-translated, native review welcome (needs system Indic font)
thไทยmachine-translated, native review welcome (needs system Thai font)
trTürkçemachine-translated, native review welcome
ukУкраїнськаmachine-translated, native review welcome
viTiếng Việtmachine-translated, native review welcome
zh简体中文machine-translated, native review welcome (needs system CJK font)

Latin / Cyrillic / Greek locales render with eframe's bundled Inter/Hack fonts. The eleven non-Latin locales (zh, ja, ko, ar, fa, he, hi, bn, ta, te, th) need a system-installed font that covers their script. Modern Windows / macOS / Linux desktops ship one out of the box:

ScriptWindowsmacOSLinux (Noto)
CJK SimplifiedMicrosoft YaHei UIPingFang SCNoto Sans CJK SC
JapaneseYu Gothic UIHiragino SansNoto Sans CJK JP
KoreanMalgun GothicApple SD Gothic NeoNoto Sans CJK KR
Arabic / PersianSegoe UI + TahomaGeeza ProNoto Sans Arabic
HebrewSegoe UIArial HebrewNoto Sans Hebrew
Indic (all scripts)Nirmala UIDevanagari Sangam MNNoto Sans Devanagari / Noto Sans Bengali
ThaiLeelawadee UIThonburiNoto Sans Thai

At startup the GUI consults fontdb to find one and appends it to egui's fallback chain; nothing is bundled into the binary. If your distro lacks the relevant Noto package, glyphs will render as tofu — install fonts-noto-cjk / fonts-noto-arabic / fonts-noto-hebrew / fonts-noto to fix.

See CONTRIBUTING.md § Translations for the native-review recipe — PRs welcome.

Features

  • Three protocols in one tool: SMTP (via lettre), IMAP and POP3 (hand-rolled over rustls so we own the full wire trace).
  • IT-actionable diagnostics: every server response is parsed and enriched with a human explanation. Microsoft 365's most painful codes (5.7.60 SendAsDenied, 5.7.139 Basic-Auth-disabled, 5.7.57 unauthenticated MAIL FROM, 5.7.708 IP-reputation block, …) are translated to "what to ask IT to change".
  • Provider presets for the eleven mail services people actually use: Outlook.com / Hotmail, Microsoft 365, Gmail / Google Workspace, Yahoo Mail, iCloud / Apple Mail, Proton Mail (Bridge), Fastmail, Zoho Mail, AOL Mail, GMX / Mail.com, and Yandex Mail — pick one from the Provider preset menu and the SMTP / IMAP / POP3 host, port, and security fields fill themselves in. Each preset carries a small note about app-password or Bridge requirements where they apply.
  • Profiles in a human-readable TOML file (smtp_test_tool.toml) auto-loaded from the executable's directory, so "verify the last-known-good settings still work" is one click.
  • DNS-side audit (feature dns): MX / SPF / DMARC / DKIM lookups, MX-host A/AAAA resolution, and IT-actionable hints sorted by severity (Critical / Warning / Info) — catches the ~90% of mail-flow failures that are actually DNS misconfiguration (missing MX, MX with no A record, +all SPF, missing or p=none DMARC, a revoked or weak <1024-bit DKIM key). DKIM selectors can't be enumerated from DNS, so the audit probes a built-in common-selector list by default (Microsoft 365, Google, SendGrid, …) or exactly the selectors you pass with --dkim-selector; --no-dkim skips it. CLI: smtp-test-tool dns (--json for machines; non-zero exit on any Critical hint, for shell-script alerting). GUI: a DNS check tab that audits on a background thread.
  • OAuth2 device-code flow for Microsoft 365 (feature oauth, RFC 8628): mint an XOAUTH2 token without storing a password. CLI: smtp-test-tool oauth-login --user prints a URL + code, polls until you authorise in the browser, then stores the refresh token in the OS keychain so later runs auto-mint a fresh access token. GUI: device-code login wired into the credentials block.
  • Accessibility is the baseline, not the goal. The GUI follows the OS dark/light setting on Windows, macOS, and Linux; colour is never the only signal (every [ PASS ] / [ FAIL ] is also textual); contrast ≥ 7:1 (WCAG 2.2 Level AAA); AccessKit is enabled for screen-reader support.
  • One binary per OS, no installer required.

Install

Windows: WinGet or Scoop

winget install StruisICT.SmtpTestTool

scoop bucket add struisict https://github.com/StruisICT/scoop-bucket
scoop install smtp-test-tool

macOS / Linux: Homebrew

brew tap struisict/tap
brew install smtp-test-tool

The tap and Scoop bucket are auto-updated by packaging/ on every release — so brew upgrade / scoop update always pulls the newest version.

Download a prebuilt binary

Grab the latest release for your OS from GitHub Releases.

OSFile
Windows (x86_64)smtp-test-tool-x86_64-pc-windows-msvc.zip
macOS (Apple Silicon)smtp-test-tool-aarch64-apple-darwin.tar.gz
macOS (Intel)smtp-test-tool-x86_64-apple-darwin.tar.gz
Linux (x86_64)smtp-test-tool-x86_64-unknown-linux-gnu.tar.gz

Each archive contains both smtp-test-tool (CLI) and smtp-test-tool-gui (GUI).

Verify your download (optional but recommended). Every release archive ships with a SLSA build-provenance attestation, so you can confirm it was built by this repository's CI and not tampered with:

gh attestation verify smtp-test-tool-x86_64-pc-windows-msvc.zip \
  --repo StruisICT/smtp-test-tool

With Cargo

cargo install smtp-test-tool          # CLI + GUI
cargo install smtp-test-tool --no-default-features  # CLI only

Usage

CLI

# First run with built-in Outlook.com defaults
smtp-test-tool --user me@outlook.com

# Write a starter config file next to the binary
smtp-test-tool init

# Use a saved profile
smtp-test-tool --profile production

# List profiles in the loaded config file
smtp-test-tool profiles

# Verbose diagnostic trace
smtp-test-tool --log-level debug

# Audit a domain's mail DNS (MX / SPF / DMARC / DKIM); --json for machines
smtp-test-tool dns example.com
# Probe a specific DKIM selector instead of the common-selector list
smtp-test-tool dns example.com --dkim-selector selector1

# Microsoft 365 device-code login: stores a refresh token in the keychain
smtp-test-tool oauth-login --user me@contoso.com

The exit code is 0 if every enabled protocol passes, 1 if any fail, 2 on an internal/configuration error — handy for monitoring and cron.

GUI

Double-click smtp-test-tool-gui (or smtp-test-tool-gui.exe). The form pre-fills with Outlook.com defaults; any smtp_test_tool.toml next to the binary is loaded automatically.

Config file (smtp_test_tool.toml)

active = "default"

[profiles.default]
user = "me@example.com"
smtp_host = "smtp-mail.outlook.com"
smtp_port = 587
smtp_security = "starttls"
imap_host = "outlook.office365.com"
imap_port = 993
imap_security = "ssl"
pop_host = "outlook.office365.com"
pop_port = 995
pop_security = "ssl"
pop_enabled = false

[profiles.on-prem]
user = "svc-monitor@corp.local"
smtp_host = "mail.corp.local"
smtp_port = 25
smtp_security = "starttls"
imap_host = "mail.corp.local"
imap_port = 143
imap_security = "starttls"
ca_file = "/etc/ssl/corp-internal-ca.pem"

Passwords and OAuth tokens are never written to the config file. They live in memory for the current session, or - on opt-in - in the native OS keychain:

  • The GUI's Servers tab has a Save password to keychain / Forget keychain entry button pair under the credentials block.
  • The CLI exposes --keychain-load (look up at startup) and --keychain-save (write after a successful test), plus a keychain status|forget subcommand.
  • Backed by Windows Credential Manager, macOS Keychain, or Linux Secret Service via gnome-keyring / KWallet. Real at-rest encryption, gated by the OS unlock prompt - unlike base64.

Say cargo build --no-default-features --features gui to ship a build without the keychain code (skips the keyring crate and, on Linux, the libdbus-1-dev runtime dependency).

Example diagnostic output

2026-05-19T08:04:11Z  INFO smtp  | SMTP target smtp.office365.com:587 (starttls)
2026-05-19T08:04:11Z  INFO smtp  | TCP connection established
2026-05-19T08:04:11Z  INFO smtp  | STARTTLS negotiated, TLSv1.3
2026-05-19T08:04:12Z  ERROR smtp | SMTP AUTH FAILED
2026-05-19T08:04:12Z  ERROR smtp |   Server replied 535: 5.7.139 Authentication unsuccessful, basic authentication is disabled
2026-05-19T08:04:12Z  ERROR smtp |     ESC 5.7.139: Authentication unsuccessful, the request did not meet the criteria.
2026-05-19T08:04:12Z  ERROR smtp |     -&gt; Action: Conditional Access policy denied the login (location, device, MFA).

That second-to-last line is what you forward to IT.

Building from source

Requires Rust 1.92 or newer (stable). The egui ecosystem sets this floor; building CLI-only with --no-default-features would in practice work on slightly older toolchains.

git clone https://github.com/StruisICT/smtp-test-tool
cd smtp-test-tool
cargo build --release
# CLI:  target/release/smtp-test-tool
# GUI:  target/release/smtp-test-tool-gui   (built when `gui` feature is on, default)

Linux build dependencies (for the GUI)

sudo apt install -y \
  libxkbcommon-dev libwayland-dev \
  libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev \
  libgl1-mesa-dev libegl1-mesa-dev libfontconfig-dev

Project layout

src/
├── lib.rs            re-exports + Outlook defaults
├── config.rs         TOML config with named profiles
├── diagnostics.rs    server-response -&gt; human hint translators
├── providers.rs      built-in provider presets (Outlook, Gmail, ...)
├── tls.rs            rustls ClientConfig builder
├── smtp.rs           SMTP test (lettre)
├── imap.rs           IMAP test (hand-rolled on rustls)
├── pop3.rs           POP3 test (hand-rolled on rustls)
├── dns.rs            MX / SPF / DMARC / DKIM audit    (feature `dns`)
├── oauth.rs          M365 device-code flow (RFC 8628) (feature `oauth`)
├── keystore.rs       OS keychain backing            (feature `keychain`)
├── i18n.rs           translation registry + key lookup
├── locale.rs         OS-locale detection
├── fonts.rs          system-font discovery for non-Latin scripts
├── theme.rs          OS dark/light follow + WCAG AAA palettes
├── runner.rs         orchestrator (run enabled protocols, summarise)
└── bin/
    ├── cli.rs        clap-based CLI
    └── gui.rs        eframe / egui GUI

See AGENTS.md for the working agreement every contributor (human or AI) must follow.

Contributing

Issues and PRs welcome. Read AGENTS.md and CONTRIBUTING.md first — they encode the non-negotiable bits (WCAG 2.2 AAA, dark+light mode, atomic conventional commits, latest-stable deps verified against the registry).

License

Dual-licensed under either of

  • Apache License, Version 2.0 (LICENSE-APACHE)
  • MIT license (LICENSE-MIT)

at your option.

Unless you explicitly state otherwise, any contribution you submit for inclusion shall be dual-licensed as above, without any additional terms or conditions.