docs: name Groundmail among SMTP relay examples

Signed-off-by: kurtis tryber <kurtis@supersend.io>

Author: Ktryberceo

apps/docs/content/docs/platform/self-hosting/email.mdx

@@ -57,7 +57,7 @@ Credentials use the AWS default provider chain: environment/shared configuration
 </Tab>
 <Tab value="SMTP">
 
-Use a reachable relay such as Postfix, SendGrid, Mailgun, Google Workspace SMTP relay, or a local test relay:
+Use a reachable relay such as Postfix, SendGrid, Mailgun, Groundmail, Google Workspace SMTP relay, or a local test relay:
 
 ```bash
 SMTP_HOST=smtp.example.com