How can I prevent customer emails from landing in spam?

Does anyone know what I can do to fix this problem.. is it even fixable?
Everytime Shopify sends an email to a customer whether it be “thanks for placing an order” or “Local pick up is ready” they are being sent to everyones junk/spam folder! Ive had to blast post on my social media to have people who weren’t coming for pickups for days, to check there junk and spam folders.

This is getting pretty awful!

help please

Please setup so your store send 1 email only to the same email every 24hrs.

would you be able to explain how I could do that?