What is RustMailer used for?

RustMailer is self-hosted email middleware, written in Rust, that gives applications one API for IMAP, SMTP, Gmail API and Microsoft Graph mail sync and sending. It is a good fit for adding mailbox sync to a SaaS product, and transactional email for CRMs and e-commerce.

Is RustMailer open source?

Yes. RustMailer is open source under a custom licence. Its source code is on GitHub at rustmailer/rustmailer and is written mainly in Rust.

Yes. RustMailer is open source, so the software itself is free to use under the terms of its own licence. Paid plans are also available, starting at $199 per year.

Can I self-host RustMailer?

Yes. RustMailer can be self-hosted on your own server or infrastructure.

What is RustMailer an alternative to?

RustMailer is an open-source alternative to Nylas.

Is RustMailer actively maintained?

Yes. The most recent commit to RustMailer was on 23 September 2026, and the latest release is 1.7.3, published on 16 September 2026. The project has 508 stars on GitHub.

RustMailer: open-source alternative to Nylas

About RustMailer

RustMailer is a self-hosted service that sits between your application and mail providers. Instead of wiring up IMAP, SMTP, Gmail API and Graph API clients separately, developers call a single service that handles account synchronization, caching and delivery. It is written in Rust.

It polls and caches multiple IMAP accounts, sends mail over SMTP with template support, and dispatches events through webhooks or message queues. Repository topics point to gRPC and OpenAPI interfaces, and the README suggests uses such as multi-account sync in SaaS products, transactional email from CRMs, open and click tracking, and support software that needs live notifications.

Because it runs on your own infrastructure, it suits teams in regulated areas such as fintech and healthcare that want auditable email workflows, and it works with any programming language through its API. The licence is listed as other, so check the repository terms before commercial use.

Key features

Unified API for IMAP, SMTP, Gmail and Graph
Multi-account IMAP polling and caching
SMTP sending with email templates
Webhook and message queue event dispatch
Open and click tracking via webhooks
gRPC and OpenAPI interfaces

Good fit for

→Adding mailbox sync to a SaaS product
→Transactional email for CRMs and e-commerce

Built with: Rust
Tags: email; imap; smtp; gmail-api; self-hosted; rust; middleware; webhooks; microsoft-graph

RustMailer: questions and answers

What is RustMailer used for?: RustMailer is self-hosted email middleware, written in Rust, that gives applications one API for IMAP, SMTP, Gmail API and Microsoft Graph mail sync and sending. It is a good fit for adding mailbox sync to a SaaS product, and transactional email for CRMs and e-commerce.
Is RustMailer open source?: Yes. RustMailer is open source under a custom licence. Its source code is on GitHub at rustmailer/rustmailer and is written mainly in Rust.
Is RustMailer free?: Yes. RustMailer is open source, so the software itself is free to use under the terms of its own licence. Paid plans are also available, starting at $199 per year.
Can I self-host RustMailer?: Yes. RustMailer can be self-hosted on your own server or infrastructure.
What is RustMailer an alternative to?: RustMailer is an open-source alternative to Nylas.
Is RustMailer actively maintained?: Yes. The most recent commit to RustMailer was on 23 September 2026, and the latest release is 1.7.3, published on 16 September 2026. The project has 508 stars on GitHub.