After 30 days of using the program you might encounter this message:

Demo expired

Your demo period has expired. Please obtain a valid eM Client license from http://www.emclient.com/purchase

You may access your offline data, but online synchronization and the sending of emails are disabled. Once a license is obtained, you will be able to use the product without limitations again.

This means you haven't activated a license within the period of the trial version. 

If you already registered or bought a license just take your Activation key and activate it in Menu > Help > License.

Otherwise please go register or purchase a license from our website. Please make sure to register the license to an email address that you have access to, as the license key will be sent there.