feat(connector): add SMTP2GO email connector

[fabiolooo]

📋 Description

This PR adds a new email connector for SMTP2GO, a reliable email delivery service for transactional and marketing emails.

✨ Features

• ✅ SMTP2GO API v3 integration
• ✅ Support for all standard Logto email templates
• ✅ Both text/plain and text/html content types
• ✅ Handlebars template variables ({{code}}, {{link}}, etc.)
• ✅ Auto-sync with Logto's i18n template system
• ✅ Comprehensive unit tests
• ✅ Full documentation (user & developer)

📦 Files Added

• packages/connectors/connector-smtp2go-email/
  • Source code (src/)
  • Tests (src/index.test.ts)
  • Documentation (README.md, docs/)
  • Logo (logo.svg)

🧪 Testing

• ✅ All unit tests pass (pnpm test)
• ✅ Build successful (pnpm build)
• ✅ TypeScript compilation without errors
• ✅ Follows existing connector patterns (SendGrid)

📚 Documentation

Includes:

• User-facing setup guide (README.md)
• Developer documentation (docs/README.md)
• CHANGELOG

✅ Checklist

• Code follows project conventions
• Tests added and passing
• Documentation complete
• Commit messages follow conventional commits
• Commits are signed
• No breaking changes

[github-actions]

COMPARE TO master

Total Size Diff ⚠️ 📈 +26.87 KB

Diff by File

Name	Diff
packages/connectors/connector-smtp2go-email/CHANGELOG.md	📈 +645 Bytes
packages/connectors/connector-smtp2go-email/README.md	📈 +5.09 KB
packages/connectors/connector-smtp2go-email/docs/README.md	📈 +1.41 KB
packages/connectors/connector-smtp2go-email/logo.svg	📈 +3.07 KB
packages/connectors/connector-smtp2go-email/package.json	📈 +1.65 KB
packages/connectors/connector-smtp2go-email/src/constant.ts	📈 +4.63 KB
packages/connectors/connector-smtp2go-email/src/index.test.ts	📈 +3.74 KB
packages/connectors/connector-smtp2go-email/src/index.ts	📈 +4.98 KB
packages/connectors/connector-smtp2go-email/src/types.ts	📈 +1.67 KB

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[fabiolooo]

Could you please review my PR?
@gao-sun @darcyYe

[darcyYe]

I have one concern about the response handling here.

From the SMTP2GO docs, error responses are documented with top-level error / error_code fields, and non-2xx responses should already be handled by the HTTPError branch from got.

Because of that, the additional check for response.body.data?.error does not seem to match the documented response shape. It would be better to either remove this branch or align it with the actual SMTP2GO response schema, so the implementation is easier to reason about and stays consistent with the provider docs.

[darcyYe]

One possible follow-up improvement: Logto's email template model already includes optional fields such as replyTo, and SMTP2GO supports custom headers.

If connector parity is a goal, it may be worth considering mapping replyTo to a Reply-To header via custom_headers. I do not see this as a blocker for the core SMTP2GO integration, but it looks like a reasonable completeness improvement.

[darcyYe]

The changelog still contains placeholder values:

[#xxxx](https://github.com/logto-io/logto/pull/xxxx)

This should be replaced before merge, otherwise the released package will contain a dead link / placeholder reference.