If your Mac is connected to the Internet, but Mail no longer sends or receives email messages, the issue could be with the provider of your email service. Or you could have missing or outdated settings in the Accounts section of Mail preferences (Mail > Preferences).
If Mail refers to a problem with the mail server or network
Mail might say that it’s unable to connect because of a problem with the mail server or network. For example, the message might refer to a connection that timed out, or too many simultaneous connections:
If you're connected to the Internet but the connection timed out, your email provider could be experiencing a service outage. Contact them or check their status webpage to make sure that their mail service is online. Examples of status pages:
If the message refers to the number of simultaneous connections, too many of your devices are checking your email account at the same time. Quit Mail on one or more of your other devices.
If Mail keeps asking for your email password
Learn what to do if Mail repeatedly asks for the password of your email account.
If Mail says that your account appears to be offline
Mail might say that your account appears to be offline due to a network problem.
If you're connected to the Internet but your account appears to be offline, your email settings might no longer be correct. To view your current settings in Mail, choose Preferences from the Mail menu, click Accounts, then select your email account.
OS X automatically uses the correct account settings for many email providers. You can use Mail Settings Lookup to view those settings, or get the settings directly from your email provider. Then compare them to the settings you see in Mail preferences.
If email doesn't arrive as soon as you expect
Incoming or outgoing email might take longer to arrive than you expect, or it might arrive on one device before arriving on another device.
Email delivery is scheduled by your email provider, and delivery time could also be affected by your Internet provider. If you often experience significant email delays, contact your email provider or Internet provider. If the delays occur only when communicating with a particular person, that person may need to contact their email provider or Internet provider.
If you still can’t send or receive email
Mail Connection Doctor might be able to tell you more about the issue.