Like many other e-mail clients, Apple's Mail program can be set to only check for messages when you request it manually. This can be convenient if you would prefer to avoid constant new-message alerts, or are not connected to the Internet and do not wish to get warnings about network problems. But sometimes even when set to manual the program will continue to check for messages automatically.
Apple's Mail e-mail client can be used for a variety of Mail services, including the classic POP and IMAP services, Exchange, and iCloud mail. The program's default setting is to check for new messages once every 5 minutes, but you can change this to a different interval by going to the General section of Mail's preferences and setting the "Check for new messages" option to the desired interval.
One option in this menu is to manually check for messages. Setting it to manual updates in this menu should mean that you will need to click the Get Mail toolbar icon in order to get new messages. But sometimes even if you have this option checked, the system will continue to automatically retrieve new messages. If this happens, you may notice it gets messages from some of your accounts and not others, indicating the setting is only working for specific accounts.
If you are encountering this problem, then you can try the following:
- Check for the IDLE command
In IMAP e-mail accounts, the IDLE command is an option for pushing real-time updates to clients, and is a basis for many "push notification" features of Mail accounts. The most common reason why the program will continue to automatically retrieve new mail is that this feature is enabled. So, if you disable automatic e-mail retrieval, be sure to also disable this command. To do this, for each of your accounts, select the account and then in the Advanced section be sure to uncheck the option to "Use IDLE command if the server supports it."
- Remove account from automatic message retrieval
While the setting in General preferences to disable automatic message retrieval should apply to all e-mail accounts, you can also individually remove your accounts from this routine. In the same Advanced tab where you find the IDLE command, uncheck the option to include each account when automatically checking for new messages. Then the accounts should only be accessed if you click the Get Mail button in the toolbar.