ImapKit

ImapKit is a library for test suites. It starts a strict IMAP mail server in the same process, so developers can see whether an email client holds up against a real mail protocol. Each test starts a fresh server in milliseconds, with the mailboxes, users and extensions it needs, and the test can change the server while the client stays connected.

What ImapKit does

• Protocol support: IMAP4rev1 and IMAP4rev2, with more than 50 extensions such as IDLE, CONDSTORE and QRESYNC, switched on per server.
• Live server changes: adds messages, changes flags, resets UIDVALIDITY and disconnects sessions while a client is connected.
• Scripted faults: reproduces late responses, throttling, autologout and dropped connections, and rejects input that breaks the standards.
• Language access: runs as a command with a REST API, so tests written in Python, Go or other languages can drive it.

Who it works with

It is built for teams writing automated tests for mail client software. It is a test tool, not a mail server for real users.

Key facts

• Installation: from npm
• Licence: MIT
• Operator: Postal Systems OÜ, named in the site footer
• Presented: 8 October 2026, on Hacker News by the maker