A full-featured email server that fits in a 6 MB Docker image and idles at ~9 MB of RAM. One binary. No dependencies. No Postfix, no Dovecot, no MySQL, no Redis.

SMTP in, SMTP out, IMAP, webmail, DKIM signing, delivery queue — everything you need to send and receive email, backed by a single SQLite file.

Perfect for homelabs, developer testing, self-hosted projects, and AI agents that need to send or receive email without spinning up an entire mail stack.

• Inbound SMTP — receive mail from the internet (port 25)
• SMTP Submission — send mail from email clients (port 587, AUTH PLAIN)
• IMAP — read mail from any IMAP client (port 993)
• Webmail — dark-themed web UI with compose, reply, forward, attachments
• DKIM — automatic key generation and message signing
• TLS — none, Let's Encrypt autocert, or manual certificate
• SQLite — single-file database, zero external dependencies
• Queue — outbound delivery with exponential backoff retries
• Docker — single scratch-based image, 6 MB

# docker-compose.yml
services:
  picomailgo:
    image: ghcr.io/ddalcu/picomailgo:latest
    ports:
      - "2525:2525"
      - "8080:8080"
      - "5587:5587"
      - "9993:9993"
    volumes:
      - mail-data:/data
    environment:
      MAIL_DOMAIN: localhost
      DATA_DIR: /data
      JWT_SECRET: "replace-with-a-random-secret"
    restart: unless-stopped

volumes:
  mail-data:

docker compose up -d

Open http://localhost:8080 to access webmail.

docker run \
  -p 2525:2525 -p 8080:8080 -p 5587:5587 -p 9993:9993 \
  -v mail-data:/data \
  -e MAIL_DOMAIN=localhost \
  -e JWT_SECRET=replace-with-a-random-secret \
  -e DATA_DIR=/data \
  ghcr.io/ddalcu/picomailgo:latest

For your domain (e.g. example.com) with mail server at mail.example.com:

; MX record — tells the world where to deliver mail for @example.com
example.com.    IN  MX  10  mail.example.com.

; A record — points your mail hostname to your server IP
mail.example.com.  IN  A  203.0.113.1

; SPF — authorizes your server to send mail for this domain
example.com.    IN  TXT  "v=spf1 a:mail.example.com -all"

; DKIM — PicoMailGo prints the DNS record value at startup
default._domainkey.example.com.  IN  TXT  "v=DKIM1; k=rsa; p=..."

; PTR (reverse DNS) — set via your hosting provider
203.0.113.1  IN  PTR  mail.example.com.

The DKIM public key is logged at startup. Copy the record value into your DNS.

go build -o picomailgo ./cmd/picomailgo
./picomailgo

Requires Go 1.24+.

• SearchMessages only filters by flags — ignores SeqNum, Uid, Since, Before, Larger, Smaller, Header, Body, Text, Not, Or criteria
• SearchMessages sequence number mapping is wrong when uid=false with flag filters — counter only counts filtered messages instead of all mailbox messages
• CopyMessages doesn't copy message_flags to the destination — copied messages lose \Seen, \Flagged, etc.
• DeleteMailbox may orphan messages and message_flags rows — verify DB schema has ON DELETE CASCADE
• Envelope only populates Date, Subject, From, To — missing Cc, Bcc, ReplyTo, Sender, InReplyTo, MessageId (needed for threading)
• ListMailboxes ignores subscribed parameter — LSUB and LIST return identical results

Apache 2.0 — see LICENSE.