How do I set up a trigger email notifying customers of a delay in shipping for everyone who has pre-ordered an item?

For tasks that require email notifications to be sent to our merchants’ customers. We highly recommend Shopify Email Apps

For tasks that require email notifications to be sent to our merchants’ customers. We highly recommend Shopify Email Apps whose primary focus is to assist Shopify merchants to trigger automated emails effectively. Below are some of these Email Solutions listed on the Shopify App Store : 

  1. Klaviyo https://apps.shopify.com/klaviyo-email-marketing 
  2. Seguno https://apps.shopify.com/seguno 
  3. Back in Stock:Customer Alerts, SureSwift Capital https://apps.shopify.com/back-in-stock
  4. Back in stock ‑ Restock notify https://apps.shopify.com/back-in-stock-zooomy  

Useful guides and information related to Shopify email automation:

https://www.klaviyo.com/blog/communicate-shipping-delays-coronavirus

https://www.youtube.com/watch?v=NNISBCnCkkw

https://keeganedwards.com/how-to-connect-mailchimp-to-shopify/