Geo-Routing — smart-mailto

How It Works

1. Collect Signals

Two browser APIs, zero network:

Intl.DateTimeFormat().resolvedOptions().timeZone— IANA timezone string (e.g., Europe/Moscow)
navigator.language — BCP 47 language tag (e.g., ru-RU)

2. Map to Region

Timezone is matched against a curated map of 180+ timezone entries:

Europe/Moscow → ru (Russia/CIS)
Asia/Tokyo → jp (Japan)
America/New_York → us (United States)

3. Order Providers

Each region maps to a prioritized provider list:

Russia → Yandex, Mail.ru, Rambler, Gmail
Japan → Yahoo! Japan, iCloud, Gmail, docomo
Germany → GMX, WEB.DE, T-Online, Gmail

4. Fallback Chain

Resolution order when no geo signals are available:

Custom providers (injected by user)
Persisted preference (localStorage)
Email domain detection
preferredProvider override
Geo-ordered default list

Timezone Coverage

smart-mailto maps 180+ IANA timezones to 20+ regional provider configurations. Coverage prioritizes regions with strong local email providers:

Russia / CIS

Timezones: Europe/Moscow, Asia/Yekaterinburg, ...

Providers: Yandex, Mail.ru, Rambler

Japan

Timezones: Asia/Tokyo, Asia/Seoul

Providers: Yahoo! Japan, iCloud, docomo

Germany

Timezones: Europe/Berlin, Europe/Vienna

Providers: GMX, WEB.DE, T-Online

France

Timezones: Europe/Paris

Providers: SFR, Free, Orange, La Poste

Poland

Timezones: Europe/Warsaw

Providers: Onet, WP, O2, Interia

China

Timezones: Asia/Shanghai, Asia/Hong_Kong

Providers: QQ, 163, Alibaba

India

Timezones: Asia/Kolkata

Providers: Gmail, Rediff, Zoho

South Korea

Timezones: Asia/Seoul

Providers: Naver, Kakao, Nate

Brazil

Timezones: America/Sao_Paulo, ...

Providers: Gmail, Outlook

Privacy & Performance

Zero Network Requests

Unlike IP geolocation services that send user data to third-party servers, smart-mailto computes location entirely in-browser. No cookies, no beacons, no external API calls. The user's location never leaves their device.

Sub-Millisecond Runtime

The entire geo detection pipeline — signal collection, region mapping, and provider ordering — completes in under 1ms. There is no impact on page load or click response times.

API Reference

Two functions control geo detection:

collectGeoSignals()

Returns

{
  timeZone: string;    // e.g. "Europe/Moscow"
  locale: string;      // e.g. "ru-RU"
  locales: string[];   // prioritized language tags
  isMobile: boolean;
  isIOS: boolean;
  isAndroid: boolean;
}

detectRegionLabel(signals)

Converts geo signals to a human-readable region label:

Example outputs

Europe/Moscow → Russia/CIS
Asia/Tokyo → Japan
America/New_York → Global
Asia/Kolkata → India

For the complete API reference, visit the Technical Specs page.