Sync Email across Devices

Once upon a time, most people used a single computer for email. Your email client would connect to your email server, download all your messages onto the computer, and then delete them from the server. And that was fine because you used only one computing device, so where else would your email messages be?

Nowadays, that approach seems quaint. Most of us use multiple devices to check our email, and we typically expect to see exactly the same messages—sorted into the same mailboxes and with the same status (read/unread, forwarded, replied to, or flagged)—on each one.

If you always use a Web browser to check your email (for example, with a Gmail account), your email is stored only in the cloud—so syncing is irrelevant, and there’s nothing for you to see here. However, if you use a client app on OS X or iOS such as Apple Mail, Microsoft Outlook, or Thunderbird to check your mail, you’ll probably want to be sure you keep everything in sync.

Even then, if you use IMAP, Exchange, and/or iCloud email accounts exclusively, you need do nothing more than confirm a few settings—these protocols are designed to keep everything in sync for you. If you use POP, you have a harder row to hoe.

Sync Email with iCloud

Mac (Apple Mail): Go to System Preferences > iCloud. Make sure you’re signed in and Mail is selected.
iOS Device (Mail): Go to Settings > iCloud. Make sure you’re signed in and Mail is turned on.
Other IMAP Client: Go to the app’s account settings and either select an existing iCloud account or create a new account. Fill in your settings as described on this support page.

Sync Settings with iCloud

iCloud can also sync other email-related data across Macs (only), as long as the appropriate checkbox in System Preferences > iCloud is selected:

iCloud Drive: Syncs email signatures, flag names, rules, and smart mailboxes.
Keychain: Syncs account settings (such as username, password, and server addresses) for all your accounts.

Use Server-side Filters

Mail, Outlook, and most other desktop email apps have built-in rules or filters that let you process incoming mail—for example, filing less-important messages into special mailboxes or sending automatic replies if certain criteria are met.

But if you have the choice, I suggest setting up rules on your email server rather than in your client app. That way they can pre-sort email delivered to your iOS devices (which don’t have mail rules). And, you can switch clients or platforms without having to redo all your rules.

If you use iCloud for email, log in to iCloud.com, select Mail, and from the gear menu, choose Preferences > Rules to set up rules.

In Gmail, log in to your Gmail account (using this link or whichever URL you normally use if you have a Google Apps account with a custom domain). From the gear pop-up menu, choose Settings and then click Filters and Blocked Addresses.

Many other mail servers also offer Web-based configuration of rules or filters; consult your email provider for details.

Sync Email with Google

First, make sure IMAP is enabled for your Google account:

Log in to your Gmail account (using this link or whichever URL you normally use if you have a Google Apps account with a custom domain).
From the gear pop-up menu, choose Settings, and then click Forwarding and POP/IMAP.
In the IMAP Access section, make sure Enable IMAP is selected. Leave other settings unchanged.

Then set up the IMAP account in your email client of choice. Use your full Gmail address as the username and the following server addresses:

IMAP: imap.gmail.com
SMTP: smtp.gmail.com

Sync Email with Exchange

Apple Mail (Mac): Go to System Preferences > Internet Accounts. If your account is not already listed, click Exchange and follow the prompts to configure it. Then check your email with Apple Mail.
Apple Mail (iOS): Go to Settings > Mail, Contacts, Calendars. If your account is not already listed, tap Add Account > Exchange and follow the prompts. When you’re finished, use the Mail app to check your email.
Outlook (Mac): Go to Tools > Accounts, click the plus button, and choose Exchange from the pop-up menu. Then follow the prompts to set up your account.

Syncing POP Email

If you use POP accounts, syncing messages between computers is much harder. The only reliable way to do it for two Macs is to quit Mail on both machines and then copy one Mac’s entire ~/Library/Mail/V3 folder (in El Capitan) or ~/Library/Mail/V2 folder (in Yosemite or earlier) to the other’s. But this overwrites all messages on the second Mac, which may result in lost data.

Doing a bidirectional, message-by-message sync is possible but messy. You could use a synchronization utility (such as ChronoSync) to sync the two computers’ ~/Library/Mail/V3 or V2 folders—but then both copies of the envelope index, which keeps track of which messages are where, will be incorrect.

To fix them, you’d have to quit Mail, delete the three files in ~/Library/Mail/V3/MailData/ or ~/Library/Mail/V2/MailData/ whose names start with Envelope Index on each Mac, relaunch Mail, and then let it reimport all your messages. Needless to say, that’s more bother than most of us want to go through regularly!

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