E-MailRelay

E-MailRelay is a lightweight SMTP store-and-forward mail server that spools incoming messages and forwards them to an upstream smarthost or via DNS MX routing. It can also expose the spool via POP3, and is designed to be “policy-free” so you can implement custom mail policies and processing using external scripts.

Key Features

• SMTP server for spooling inbound email and forwarding queued mail to a smarthost
• Store-and-forward workflow (server spools; client forwards) with polling and retry support
• Optional POP3 server to retrieve messages directly from the spool directory
• Scriptable hooks for address verification and message filtering/processing
• Can integrate with SpamAssassin (spamd) for spam marking or rejection
• Single-process, non-blocking I/O design for efficient resource usage
• Cross-platform usage patterns (commonly deployed on Unix-like systems and Windows)

Use Cases

• Mail relay for intermittently connected networks (queue locally, forward when online)
• Simple inbound mail spool with POP3 retrieval for small environments or appliances
• Custom mail processing gateway using external filters (rewrite, copy, deliver to maildir)

Limitations and Considerations

• Does not provide IMAP directly; IMAP typically requires delivering to maildir and using a separate IMAP server
• Being policy-free means common behaviors (retry/bounce strategy, delivery rules) may require scripting and operational setup

E-MailRelay is a pragmatic choice when you need a small, efficient SMTP spool-and-forward service with optional POP3 access. It fits especially well in setups where you want minimal dependencies and prefer implementing mail-handling logic via scripts rather than a large integrated mail stack.