This task requires the System Administrator or System Customizer security role A defined set of privileges. The security role assigned to a user determines which tasks the user can perform and which parts of the user interface the user can view. All users must be assigned at least one security role in order to access the system. or equivalent permissions. More information about specific permissions and performing this task while offline: E-mail Permissions
In the Navigation Pane, click Settings, click Administration, and then click System Settings.E-mail tab.
Make changes to the following options:
Use tracking token
Select this check box to use tracking tokens and to configure how they are displayed in the Subject line of the e-mail messages. Using tracking tokens increases the accuracy of determining if a new record is related to an existing, tracked record. When you change the e-mail prefix, up to 256 characters are saved as history. Long prefixes or too many prefix changes may cause lost data in history.
Track e-mails sent between CRM users as two activities Select this option to create two e-mail activities between Microsoft Dynamics CRM Online users, one for the sender and one for the recipient.
Set E-mail form options Select the options for e-mail forms.
Set file size limit for attachments
Increase or decrease the allowed size of files that can be attached to records.
To save your changes and close the dialog box, click OK.