We are able to send emails to other domains. But we are unable to send internal emails and also we are unable to receive incoming emails from other domains.

On opening the que emails message in the Sent Folder we see there is an error with a reason "Host not reachable"

We use NameCheap.com for DNS manager and we have the MX Records and the SPF Records in place in the DNS but thy are not getting verified.

Can someone please help here?