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