Zoho Mail Add-on - Error Messages

Mail Box (yourmailID) you have configured earlier is not reachable. Please select a new "Mail Box".
One of the instances why this message will display is when you change the Default Email ID in your Zoho Mail settings (Settings > Custom Settings > My Preferences).

The Zoho Mail server is currently unavailable. Please try after a while
Emails will not be displayed if the mail servers are not accessible. In the event of this scenario please wait for a couple of minutes before you try accessing your email.

Your account status in Zoho is still not confirmed
If your account status has not been confirmed/verified in Zoho, then mail will not be displayed. Please do the following to confirm your status:

1. Select http://accounts.zoho.com and click on My Email IDs.
2. Click on the Resend Confirmation icon.
3. Access your mail and click on the confirmation link.
4. Visit mail.zoho.com to activate the mail account.
5. Configure mail in Zoho CRM.

Your email is queued in Zoho Mail - Outbox
The Outbox option keeps your Emails in queue for a specified time interval before sending from the Zoho Mail. If you enabled this option, sent Emails will be listed under the Emails section after a few minutes.