Work offline
An email account can be offline (not connected to the Internet) if your Internet connection is disrupted, a mail server experiences problems, or you purposely take it offline (for example, prior to air travel). When your account is offline you can’t get or send messages, but you can write messages to send later.
Take all accounts offline: Choose Mailbox > Take All Accounts Offline.
Take a specific account offline: Choose Mailbox > Online Status > Take [account] Offline.
Write messages offline: Write your message as usual but save it as a draft, then send it later when the account’s online again. Or write the message, then click Send. Mail stores your message in the Outbox, then automatically sends it when the account’s online.
Take all accounts online: Choose Mailbox > Take All Accounts Online.
Take a specific account online: Choose Mailbox > Online Status > Take [account] Online.