mails are not working - "HTTP Status 401 - Unauthorized access"

mails are not working - "HTTP Status 401 - Unauthorized access"

I am getting error when i trying to access my mailbox. Same error see all my colleagues. all other services are working ok, only Mail service is crashed.

here is error message. please help ASAP. Thanks.

HTTP Status 401 - Unauthorized access

type Status report

message Unauthorized access

description This request requires HTTP authentication (Unauthorized access).

ZGS