Thanks for using Apple Support Communities.
For more information on this, take a look at:
OS X Mail: Troubleshooting sending and receiving email messages
First confirm these three things with your email service provider (ESP)
Contact your ESP's support staff (or visit the ESP's support website), then confirm the following:
- The ESP's email servers are up and running.
- The email account password you are using is correct, and it is being accepted.
- That your email account is capable of sending and receiving email messages; it has not been deactivated.
Open Mail Connection Doctor
In Mail, choose Window > Connection Doctor.
click to a specific topic that lists your issue.
Best of luck,