isync

CLIMail tool

Command line program (mbsync) that syncs IMAP mailboxes with local Maildir folders in both directions.

isync is the project name; the program is called mbsync. It keeps a local Maildir copy of IMAP folders and propagates new messages, deletions and flag changes both ways, using one state file per mailbox pair. It is a common companion to Maildir-based clients such as NeoMutt, aerc, mu4e and notmuch. Sending mail is out of scope; pair it with an SMTP tool such as msmtp.

Type: Mail tool
Interface: Command-line tools and prompts
Systems: Runs on Linux, macOS and BSD, on Windows through WSL, on Android through Termux.
Language: C
License: GPL 2.0 or later
Latest version: 1.5.1
Maintained: Yes
Website: isync.sourceforge.io
Source: sourceforge.net/p/isync/isync
Documentation: isync.sourceforge.io

Install

System	Support	Install
Linux	Native	apt`sudo apt install isync` dnf`sudo dnf install isync` pacman`sudo pacman -S isync` apk`sudo apk add isync`
macOS	Native	Homebrew`brew install isync` MacPorts`sudo port install isync`
Windows	Through WSL	WSL`sudo apt install isync` No native Windows build; use WSL.
BSD	Native	FreeBSD pkg`pkg install isync` OpenBSD`pkg_add isync`
Android	Through Termux	Termux`pkg install isync`

Protocols and features

Protocols
Protocol	isync
IMAP	Yes
POP3	No
SMTP	No
JMAP	No
Maildir	Yes
mbox	No
notmuch	No

Features
Feature	isync
OpenPGP	No
S/MIME	No
OAuth2 sign-in	via a Cyrus SASL XOAUTH2 plugin and PassCmd
Threads	No
Search	No
HTML mail	No
Mouse	No
Multiple accounts	Yes
Offline use	keeps a full local Maildir copy
Calendar	No
Contacts	No
Vim-style keys	No
Configuration	~/.mbsyncrc or ~/.config/isyncrc text file

Pros and cons

Pros

Two-way sync of messages, deletions and flags between IMAP and Maildir
PassCmd reads the password from any command, such as pass or gpg
Packaged for nearly every Linux distribution, macOS, the BSDs and Termux

Cons

Version 1.5 renamed options (SSLType to TLSType), so older guides need edits
Only IMAP and Maildir; no POP3 and no sending
No built-in daemon or IDLE watch; runs from cron, a timer or the mail client

Use isync with Forward Email

How isync fits with a Forward Email mailbox. Replace you@example.com with your alias and the password command with your own. The same settings work with any provider once the server names change.

~/.mbsyncrc

# Sync a Forward Email mailbox to ~/Mail/forwardemail (run: mkdir -p ~/Mail/forwardemail)
# TLSType needs isync 1.5 or newer; on 1.4 write "SSLType IMAPS" instead.
IMAPAccount forwardemail
Host imap.forwardemail.net
Port 993
User you@example.com
PassCmd "pass show forwardemail/you@example.com"
TLSType IMAPS

IMAPStore forwardemail-remote
Account forwardemail

MaildirStore forwardemail-local
SubFolders Verbatim
Path ~/Mail/forwardemail/
Inbox ~/Mail/forwardemail/INBOX

Channel forwardemail
Far :forwardemail-remote:
Near :forwardemail-local:
Patterns *
Create Both
Expunge Both
SyncState *

# Then run: mbsync forwardemail

Protocol	Server	Port	Security
IMAP	`imap.forwardemail.net`	993	SSL/TLS
POP3	`pop3.forwardemail.net`	995	SSL/TLS
SMTP	`smtp.forwardemail.net`	465	SSL/TLS
SMTP	`smtp.forwardemail.net`	587	STARTTLS

Username: your full alias address, such as you@example.com. Password: the one shown by Generate Password next to the alias in your Forward Email account. Folders: INBOX, Drafts, Sent Mail, Trash, Spam and Archive.

Prefer no config at all? Forward Email's terminal app signs in with your account and has mail, calendar and contacts in one program.

Questions

Does isync work on Windows?

Not natively. It runs in Windows Subsystem for Linux (WSL). No native Windows build; use WSL.

Does isync support IMAP?

Yes, isync connects to IMAP servers directly.

Is isync open source?

Yes, under the GPL 2.0 or later.

How do I use isync with Forward Email?

Use the config in the Forward Email section on this page, saved as ~/.mbsyncrc, and replace the address and password with your own.

Sources

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