How does Google Analytics attribute conversions from email?

Google Analytics attributes conversions based on the UTM parameters in the click. If no UTMs are present it may classify the traffic as direct or unknown.

By default, Google Analytics 4 (GA4) uses a data driven attribution model which distributes credit across multiple touchpoints. The older last non direct click model can still be selected, but data driven is now the standard. This means email can receive partial credit based on its modeled contribution even if it was not the final click.