MailShrink
Safely reclaim disk space on Dovecot Maildir servers.

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MailShrink does not simply run gzip over your Maildir. It understands Dovecot Maildir metadata, preserves INTERNALDATE, validates S= metadata, uses mailbox locking, detects existing compression, performs atomic replacement, and verifies messages before removing the uncompressed copy.

Demo

Install

curl -sL https://github.com/nemke82/mailshrink/releases/latest/download/mailshrink-linux-amd64 \
  -o /usr/local/bin/mailshrink && chmod +x /usr/local/bin/mailshrink

ARM64:

curl -sL https://github.com/nemke82/mailshrink/releases/latest/download/mailshrink-linux-arm64 \
  -o /usr/local/bin/mailshrink && chmod +x /usr/local/bin/mailshrink

Works on any Linux server — Ubuntu, Debian, AlmaLinux, Rocky, RHEL, or any distro running Dovecot with Maildir storage. Single static binary, no dependencies.

Prerequisites

Dovecot with the zlib plugin. Most hosting panels already have it — run mailshrink check to verify.

# Ubuntu / Debian
apt install dovecot-core

# AlmaLinux / Rocky / RHEL
dnf install dovecot

Quick Start

1. Verify Dovecot is ready:

mailshrink check

2. See how much space you can reclaim:

mailshrink analyze

3. Get a detailed plan:

mailshrink plan example.com

4. Compress (dry-run first, then apply):

# See what would happen (no files touched):
mailshrink compress --domain example.com --folder Sent --before 2025-01-01

# Actually compress:
mailshrink compress --domain example.com --folder Sent --before 2025-01-01 --apply

How It Works

MailShrink gzip-compresses old email files in place. Dovecot's zlib plugin transparently decompresses them on read — users see no difference.

Safety first:

• Dry-run by default — compress requires --apply to modify files
• Dovecot check — verifies zlib is enabled before compressing
• Atomic operations — original file untouched until compression succeeds
• Metadata preserved — mtime (IMAP date), ownership, permissions all restored
• Maildir locking — prevents conflicts with Dovecot
• No deletion — MailShrink never deletes email

Measure, don't guess — instead of assuming "gzip saves ~20%", MailShrink samples your actual messages, compresses them in memory, and reports the real measured ratio.

Commands

Command	Description
check	Verify Dovecot + zlib plugin readiness
analyze	Scan mailboxes, sample messages, estimate savings
plan	Detailed per-account/folder breakdown
compress	Compress messages (dry-run by default, --apply to execute)
version	Print version info

Key Flags

Flag	Available On	Description
--path	all	Base scan path (default: /home)
--domain	compress	Target domain
--account	compress	Target account (user@domain)
--folder	analyze, plan, compress	Target folder (Sent, INBOX, etc.)
--before	compress	Only messages before date (YYYY-MM-DD)
--older-than	analyze, plan, compress	Age filter (2y, 6m, 90d)
--apply	compress	Required to actually modify files
--json	all	Machine-readable output
--provider	all	Force panel type (cpanel, directadmin, generic)

Supported Servers

MailShrink auto-detects your server layout:

Panel	Mail Path	Status
cPanel / WHM	/home/user/mail/domain/account/	✅
DirectAdmin	/home/user/imap/domain/account/Maildir/	✅
Custom Dovecot	Any Maildir with cur/new/tmp	✅
Plesk	/var/qmail/mailnames/domain/account/Maildir/	🔜

Production & Bulk Automation

For multi-server hosting environments, fleet automation, and scheduled maintenance, see the Production & Bulk Automation Guide:

• 📦 Ansible Deployment — Playbook to deploy and verify MailShrink across your fleet
• 📊 Mass Scanning & JQ — Auditing hundreds of accounts with high concurrency and JSON export
• ⏰ Automated Maintenance Cronjobs — Safe recurring background compression with ionice & nice
• 🚀 Pre-Migration Optimization — Shrink mail storage before server transfers
• 🛡️ Disk Monitoring & Emergency Hooks — Automated reclamation script when disk reaches 90%+

Origin

Based on the article How I Saved Gigabytes of Disk Space by Compressing Old Dovecot Maildir Emails on cPanel, which helped reclaim free disk space on production servers. MailShrink turns that manual process into a safe, automated tool.

License

MIT