Update email server in Bigcommerce

I found two messages in my spam box. One to me and one to the customer, both had a message saying,

"Hello, this is the mail server on smtp10.bigcommerce.com.

I am sending you this message to inform you on the delivery status of a
message you previously sent. Immediately below you will find a list of
the affected recipients; also attached is a Delivery Status Notification
(DSN) report in standard format, as well as the headers of the original
message.

delivery failed; will not continue trying"

So apparently, all emails sent from Bigcommerce are going to spam folders. Why is this? This has never happened in the past.

Note: This topic was created from a reply on the Problem Logging into Bigcommerce Storefront topic.