external smtp office365 configure in sendmail

exchange server migrated to office 365,after that mails are not going from rhel7.3.

Please check below error message

STARTTLS=client, relay=smtp.office365.com, version=TLSv1/SSLv3, verify=FAIL, cipher=AES256-SHA

relay=smtp.office365.com [40.101.72.130], dsn=5.0.0, stat=Service unavailable

Jan 12 10:01:35 aea75db01 sendmail[18746]: [ID 801593 mail.info] w0C71GcA018746: w0C71GcB018746: DSN: Service unavailable