In Dynamics CRM 4.0, by default, the only entities that can be sent an email via an email activity or workflow are Account, Contact, Lead, and User. If you want to be able to send emails to records of a custom entity, you would need complex plugins to associate your custom entity to and Account or Contact so the email could be sent from there.
However Dynamics CRM 2011 has done away with this issue, as there is now a built in, supported method for sending email to custom entities.
To enable a new entity to be able to have email sent to it, all you need to do is check the box labelled ‘Receive Email’, when creating the entity.
Note: This option can only be enabled when creating new entities.
Once you save the entity, there will automatically be an email address field created.
You can now customize the form to include the email field (by default only ‘Name’ will be displayed on the form).
You can then publish your customizations, and create a record. After saving the record you will notice the option to send E-mail on the ‘Add’ tab of the ribbon, which will create an E-mail activity that will be sent to the email address specified on the record.
Also when you are creating a workflow, you can specify a record from any custom entity in the ‘To’ field, that has this email option enabled.
That’s all there is to it! You can set this option on any custom entity you create, so that you can send email directly to records of that entity without using any complex plugins to link to contacts or accounts.