NioSmtpClient

High performance SMTP client in Java based on Netty. This client is well tested and heavily used at HubSpot.

Maven Dependency

<dependency>
  <groupId>com.hubspot</groupId>
  <artifactId>NioSmtpClient</artifactId>
  <version>1.1.0</version>
</dependency>

Features

• High performance, designed to handle many concurrent connections
• Supports TLS, pipelining, chunking, SIZE, SMTPUTF8, and other ESMTP RFCs
• Send from specific IP addresses
• Optionally keeps connections alive to send subsequent emails
• Parses the EHLO response and chooses the most-efficient sending method
• Interceptor support to modify or instrument commands
• Comprehensive unit and integration tests

Dependencies

This project depends on Java8, Netty, and Guava.

Java Docs

See http://github.hubspot.com/NioSmtpClient/1.0.0/

Notes For Developers

• NEVER execute blocking commands on an eventloop thread (i.e. CountDownLatch.await or Future.get)
  • Calls out to unknown functions (i.e. callbacks or event listeners) should always be done on isolated thread pools.
  • Slow but not necessarily blocking operations should also be avoided
• Attempt to avoid doing long running tasks on event loop threads
• Use new as sparingly as possible to avoid creating garbage:
  • Share objects when possible
  • Use netty bytebuf allocators when possible
  • Use netty recyclers for objects that can be recycled.

License

Apache 2.0