To keep project mailboxes consistent across Macs and other devices, create each project folder inside the email account on its mail server, then check that Mail’s special folders—such as Sent and Drafts—also point to server mailboxes. A folder under “On My Mac” exists only on that Mac. This guide focuses on setting up and checking those choices in macOS Mail; what syncs depends on the email account and its provider.

Decide where project mail should live

In Mail, a mailbox is a folder for messages. When you create one, the Location menu determines whether it is local or belongs to an account. Apple says account mailboxes are stored on the email server and can be accessed on other devices using that account; “On My Mac” mailboxes are only available on the Mac where they were created. Apple’s guide to creating mailboxes

For a project folder you want to see across devices, choose the correct email account as its location. For example, create Project – Redwood inside your work account rather than under “On My Mac.” If you want a nested structure, select the project mailbox as the location for a subfolder. Keep local folders for material you intentionally want to keep only on that Mac.

Create a project mailbox on the server

  1. Open Mail on your Mac and choose Mailbox > New Mailbox.
  2. In Location, choose the email account that should hold the project messages. Do not choose On My Mac for a folder that needs to appear elsewhere.
  3. Enter a clear project name and click OK.
  4. Confirm the new mailbox appears beneath the intended account in the sidebar. If you need subfolders, repeat the steps and select the project mailbox as the location.
  5. Move a small, noncritical test message into the folder. Then check that the folder and message appear when you view the same account on another device or in the provider’s webmail, if available.

Apple notes that some workplace mailboxes may be read-only, so you may not be able to create folders inside them. Server folder creation and availability are also subject to the account provider. If the intended account is missing from the Location list or the folder does not appear elsewhere, check with your email administrator or provider before trying to recreate the folder in another location. Apple’s mailbox creation instructions

Align Sent, Drafts, Trash, Junk, and Archive

A project folder can sync while the account’s special mailboxes still behave differently. On each Mac, open Mail > Settings > Accounts, select the account, then click Mailbox Behaviors. Review the choices for Drafts, Sent, Junk, Trash, and Archive. Where available, select the intended mailbox on the server. Mail’s available options vary by account type; Apple says Drafts, Sent, Junk, and Trash choices are available for IMAP accounts, while Archive selects a mailbox on the server. Apple’s Mailbox Behaviors documentation

This check matters when a sent project reply, draft, or deleted message seems to be missing on another device. A behavior set to an “On My Mac” mailbox stores those messages only on that Mac. Apple specifically advises selecting the Junk mailbox on each Mac using the account to avoid duplicate Junk mailboxes in the sidebar. Make the same choices on every Mac where you use the account; the existence of a server folder does not itself prove each Mac is configured to use it for a special behavior.

Avoid changing server or IMAP path settings by guesswork. If the correct server mailbox is not offered, Apple advises checking with the email provider before choosing another server mailbox. In Mail’s Server Settings, an IMAP Path Prefix is described as the location of mailboxes on an IMAP server; Apple says to enter or change it as directed by the provider. Apple’s Server Settings documentation

Check the setup on each device

Use this quick audit after creating the folder or changing behaviors:

  • The project mailbox appears inside the intended account in the Mac sidebar, not under “On My Mac.”
  • The same account is enabled on each device, and the project folder is visible there or in webmail.
  • On each Mac, the account’s Mailbox Behaviors point to the intended server mailboxes where those controls are available.
  • A test message moved into the project folder remains there when viewed from another device.

For iCloud Mail, Apple says custom folders are visible on devices with Mail turned on in iCloud settings. On a Mac, check Apple menu > System Settings > [your name] > iCloud > Mail and enable syncing for the Mac. Apple also documents certain Mail settings that stay up to date through iCloud Drive, including rules, signatures, and Smart Mailboxes. Those settings are distinct from the project messages and mailbox contents themselves. Apple’s iCloud Mail setup guide and guide to iCloud Mail folders

If a folder is missing or duplicated

First confirm that both devices are using the same account and that the mailbox was created under that account rather than “On My Mac.” For iCloud Mail, also check that Mail is enabled for iCloud on the device. For a non-iCloud account, consult its provider’s instructions if folders fail to appear or if special mailboxes have unfamiliar names. Do not delete a duplicate until you have confirmed which mailbox contains the messages: Apple warns that deleting a mailbox permanently deletes it and its contents. Apple’s mailbox guide

The dependable Mac workflow is to create project folders in the account, then review each Mac’s special mailbox behaviors separately. Server folders make the project’s messages available through the account on other devices; per-Mac behavior checks help ensure everyday mail actions use the intended server folders.

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