Yes, you can use a number of variables in your messages while sending mass mail from eM Client.

To add variables, right-click the message body while composing a new message and select Insert > Variable. Then you can select a number of variables from a list of available variables.

The content of the variable will be replaced by either data from your computer (such as date and time options) or from your contact's details.

Note: If you use Variables in your message and try to send it to more recipients it will always be sent as Mass Mail (feature available with paid licenses).