What is Inbucket?

Inbucket is a disposable webmail server for testing email functionality in applications. It accepts messages sent to any address and makes them accessible through a web UI, a REST API, and a POP3 server. The software includes its own SMTP and POP3 daemons and stores mail locally on disk as simple files, so no external database or mail server is needed. Deployment options include Docker containers, pre-built binaries for major operating systems, Linux packages (deb and rpm) with systemd integration, a community Helm chart for Kubernetes, and building from source. All configuration is handled through environment variables that control ports, storage backend (memory or file-based), message retention policies, mailbox naming schemes, and TLS settings. The web UI provides real-time message monitoring, MIME attachment handling, HTML email rendering, and source viewing. A Go client library is available for the REST API. The project is production-ready and released under the MIT license.

Should you self-host Inbucket?

Inbucket scores 29/100 on selfhost.directory (how scoring works) and ranks #104 of 106 in Email. It has 2 310 GitHub stars.

It shipped 2 stable releases in the past year. The latest, v3.2.0, came out on 10 October 2026. New versions land roughly every 10 months.

An official Docker image is available. It is MIT-licensed and written mostly in Go.

Its closest alternative on selfhost.directory is Listmonk (80/100, 24 017 stars). It scores higher overall, so compare the two before you pick. See Inbucket vs Listmonk side by side.

Features

Built-in POP3 server
Built-in SMTP server
Configurable message retention
HTML email preview
Load test mode
Mailbox naming strategies
MIME attachment handling
Multiple Storage Backends
Per-mailbox message cap
Real-time message monitor
REST API
TLS certificate auto-reload
Web Interface

How to configure Inbucket

INBUCKET_LOGLEVELinfoLog verbosity level
Log verbosity level
values: debug, info, warn, error
INBUCKET_LUA_PATHinbucket.luaPath to optional Lua script
Path to optional Lua script
values: file path
INBUCKET_MAILBOXNAMINGlocalMailbox naming strategy
Mailbox naming strategy
values: local, full, domain
INBUCKET_POP3_ADDR0.0.0.0:1100POP3 server listen address and port
POP3 server listen address and port
values: IP:port
INBUCKET_POP3_DOMAINinbucketPOP3 greeting domain
POP3 greeting domain
values: domain name
INBUCKET_POP3_TIMEOUT600sPOP3 idle network timeout
POP3 idle network timeout
values: duration (s, m)
INBUCKET_SMTP_ACCEPTDOMAINSDomains to accept mail for
Domains to accept mail for
values: comma-separated domains
INBUCKET_SMTP_ADDR0.0.0.0:2500SMTP server listen address and port
SMTP server listen address and port
values: IP:port
INBUCKET_SMTP_DEFAULTACCEPTtrueAccept all mail by default
Accept all mail by default
values: true, false
INBUCKET_SMTP_DEFAULTSTOREtrueStore all mail by default
Store all mail by default
values: true, false
INBUCKET_SMTP_DISCARDDOMAINSDomains to discard mail for
Domains to discard mail for
values: comma-separated domains
INBUCKET_SMTP_DOMAINinbucketSMTP HELO domain
SMTP HELO domain
values: domain name
INBUCKET_SMTP_MAXMESSAGEBYTES10240000Maximum message size in bytes
Maximum message size in bytes
values: positive integer
INBUCKET_SMTP_MAXRECIPIENTS200Maximum RCPT TO per message
Maximum RCPT TO per message
values: positive integer
INBUCKET_SMTP_REJECTDOMAINSDomains to reject mail for
Domains to reject mail for
values: comma-separated domains
INBUCKET_SMTP_REJECTORIGINDOMAINSDomains to reject mail from
Domains to reject mail from
values: comma-separated domains
INBUCKET_SMTP_STOREDOMAINSDomains to store mail for
Domains to store mail for
values: comma-separated domains
INBUCKET_SMTP_TIMEOUT300sSMTP idle network timeout
SMTP idle network timeout
values: duration (s, m)
INBUCKET_SMTP_TLSCERTcert.crtTLS certificate file
TLS certificate file
values: file path
INBUCKET_SMTP_TLSENABLEDfalseEnable STARTTLS
Enable STARTTLS
values: true, false
INBUCKET_SMTP_TLSPRIVKEYcert.keyTLS private key file
TLS private key file
values: file path
INBUCKET_STORAGE_MAILBOXMSGCAP500Maximum messages per mailbox
Maximum messages per mailbox
values: positive integer or 0
INBUCKET_STORAGE_PARAMSStorage implementation parameters
Storage implementation parameters
values: key:value pairs
INBUCKET_STORAGE_RETENTIONPERIOD24hMessage retention period
Message retention period
values: duration (m, h)
INBUCKET_STORAGE_RETENTIONSLEEP50msSleep between mailbox scans
Sleep between mailbox scans
values: duration (ms, s)
INBUCKET_STORAGE_TYPEmemoryStorage implementation
Storage implementation
values: file, memory
INBUCKET_WEB_ADDR0.0.0.0:9000Web server listen address and port
Web server listen address and port
values: IP:port
INBUCKET_WEB_BASEPATHBase path prefix for UI and API URLs
Base path prefix for UI and API URLs
values: URI prefix
INBUCKET_WEB_GREETINGFILEui/greeting.htmlGreeting HTML file
Greeting HTML file
values: file path
INBUCKET_WEB_MONITORHISTORY30Monitor remembered messages
Monitor remembered messages
values: integer >= 0
INBUCKET_WEB_MONITORVISIBLEtrueShow monitor tab in UI
Show monitor tab in UI
values: true, false
INBUCKET_WEB_PPROFfalseExpose pprof profiling endpoint
Expose pprof profiling endpoint
values: true, false
INBUCKET_WEB_UIDIRui/distWeb UI directory
Web UI directory
values: file path