mail.domainname.com not working

mail.domainname.com not working

We just noticed that we can not access our online email login anymore at mail.ourdomainname.com

Zohomail.com logins work but all our staff access mail online at mail.ourdomain.com

We initialy set this up via DNS record pointing 'mail' to zoho and it was working fine up until a few hours ago.

Please help. Thank you.