If you send newsletters or other types of emails to existing customers (or prospects), you should:
- include a link back to your site
- tag that link with campaign parameters so resulting traffic is not counted as direct
- consider pointing to a specialized welcome-back page instead of the home page
Regarding the last point, your return customers may respond better to specialized recognition on a dedicated welcome-back page than to the messaging presented to all other visitors. If you can A/B test your email campaigns, try sending only half of your emails with a link pointing to the welcome-back page (and containing separate campaign parameters) so you can compare conversions and other metrics against visitors pointed to the general home page.
For visitors to the welcome-back page, you might be tempted to skip the campaign parameters and just create an advanced segment as needed later on, but remember that this segment would only apply if the welcome-back page were viewed during the visit; it would not apply to any direct visits that occurred subsequently and bypassed the welcome-back page.
With campaign parameters, on the other hand, Google Analytics will continue to attribute subsequent direct visits to the welcome-back campaign, as long as visitors don’t delete cookies from their browsers and don’t return from another source, such as an organic search result, that overrides the campaign.