Upgrade the Yosemite system users, you can use the link diagnostics to detect the status of the user's mail, this method can be a good response to the user's email reception status, so as not to cause unnecessary losses, these several methods make it very simple.
Use Mail connection diagnostics to check the status of your Internet connection or e-mail account.
1, choose "Window" > "Connection Diagnostics".
2, check the status information, and then try to resolve any problems.
3. To view the log information when the mail tries to connect, click Show Details, and then click Check again.
4, check the Internet connection: If the "Connection status" shows a red dot, then "mail" can not connect to the Internet. Click Network Diagnostics to get help to resolve the problem.
5. Check your email account: If the account shows a red status dot (connected to the Internet), the account provider's mail server or your account settings may be having problems. Follow the instructions in the "More Information" column. To view the accounts in the accounts pane of mail preferences, click the text in the Details column.
6, after the completion, click "Check Again" to see if your operation has resolved the problem.
7. If the problem remains unresolved, please contact your account provider to verify your account details and settings.
If you contact Apple support to troubleshoot mail-related issues, you may also be asked to select the Log Connection activity check box. When selected, the system collects diagnostic information when you use mail to help Apple support understand and troubleshoot mail issues, check your computer's problems, and help improve Apple's products and services. The diagnostic information that is collected may contain personal information, including your e-mail content. If you send it to apple,apple, it will use this information according to its privacy policy and will not be shared with any other company.
To view the folder for the log file in the Finder, click Show Log. After you provide the log file to Apple support, deselect this check box to close the connection activity record. You may wish to delete the log files because they may be too large.