So we have many issues with the sub-domain that we are using with the marketing cloud. One of them is: If we want to reply to the emails from Outlook, we get an error message that says:
Undelivarable and the content is: reply-fecc157376670c7c-2139_HTML-104564539-100025066-1 wasn't found at hello.ourSubdomain.com.
Also every time a client replies to one of our emails,
@hello.ourSubdomain.com is getting appended at the end of their actual email address.
We did whitelist our IP address and this was resolved for 2 days. But later, we started getting the same errors.