Your sales channel may already send emails on your behalf when orders are marked shipped by SKULabs. When that is not the case, or you want SKULabs to email your customers when partial mark as shipped is not available you enable email notification in your store settings.
After you've enabled email notifications, if you're still experiencing issues know that SKULabs utilizes a paid transactional email service with very high deliverability statistics.
The best way to diagnose these issues is to open up an in-app conversation system window (the orange icon) and then to include an email address and order number that you're being told by the customer they did not receive the email.
Most of the time, the customer has simply lost the email in their inboxes. We have no reported issues with emails being sent to Spam on a regular basis due to the quality of the email service we use. If you are experiencing reports of tracking emails going to spam, we recommend you review your shipment notification template for common pitfalls when writing emails.