Take email accounts offline or online in Mail on Mac
You can take your email accounts offline — for example, prior to air travel — then take them back online when you’re ready.
Take email accounts offline
Go to the Mail app on your Mac.
Do one of the following:
Take all accounts offline: Choose Mailbox > Take All Accounts Offline.
Take a specific account offline (if you have more than one account): Choose Mailbox > Online Status > Take [account] Offline.
A lightning bolt icon next to an account’s mailboxes in the Mail sidebar and at the end of the Favourites bar indicates the account is offline.
When an account is offline, you can’t get or send messages, but you can write messages to send later. You can save your message as a draft and send it when your account’s online again; or click Send to store your message in the Outbox and automatically send it when your account’s online.
Take email accounts online
Go to the Mail app on your Mac.
Do one of the following:
Take all accounts online: Choose Mailbox > Take All Accounts Online.
Take a specific account online (if you have more than one account): Choose Mailbox > Online Status > Take [account] Online.