The following article is a recorded SSL security certificate error when using the native Macintosh iMail or Mac Mail programs.
The Mac Mail client is currently generating an error due to the inability to verify the certifying authority for the certificate. This issue is particular to clients' packages with the Mac OS X systems. (example, connecting to a mailbox using Outlook 2011) the Zimbra Desktop Client does not result in the certificate error; likewise, connecting to certain sites with Safari will produce a certificate error, while connecting to those same sites with Google Chrome or Mozilla Firefox on the Macintosh computer

Solution:

1. Within the System Preferences, select the Mail applet.
2. Select 'Add Another Account'
3. Select 'Add Mail Account'
4. Select Next

Enter the following information to manually configure the Zimbra account:

Account Type: IMAP
Mail server: mail.zimbraservice.com
Username: name@domain.com
Password: Your mailbox password

5. Select Next
6. Select 'Show Certificate'.
7. Click to checkmark 'Always Trust mail.zimbraservice.com when connecting to mail.zimbraservice.com'

Please note that an Apple Macintosh Administrative password may be required at this juncture in order to validate the certificate.

8. Enter the following information for the SMTP server:

mail.zimbraservice.com

9. Select 'Done'.

The account should now no longer encounter this error.


Please Note: All of our certificates are produced and signed by Thawte, which is a leading SSL certificate provider. Additionally, at this time, there is not a permanent fix to this issue. Any permanent fix that does occur will need to be part of a future OS X update from Apple.