When you set up a custom domain with Mailsuite, you may expect it to replace the mailtrack.io references used across all types of tracking. However, custom domain tracking only applies to link tracking.
This means that when you insert a tracked link in your email using Mailsuite, the link will use your custom domain. Email open tracking and PDF tracking, on the other hand, will continue to reference the standard Mailsuite domain and are not affected by your custom domain configuration.
If you notice that your custom domain appears correctly on tracked links but not on the tracking image used for email opens or on tracked PDF attachments, this is expected behavior and not a configuration issue.