Change MTA Host name

Hi There,

I am getting the following bounce back when emailing people from my Exchange 2013 server:

Remote Server returned ’550 5.7.1 <rene.fleisch@bitschnau.com<mailto:rene.fleisch@bitschnau.com>>: Recipient address rejected: Mail appeared to be SPAM or forged. Ask your Mail/DNS-Administrator to correct HELO and DNS MX settings or to get removed from DNSBLs; MTA helo: ttlcloudexch04.ttlcloud.local, MTA hostname: remote.ttlhosting.co.uk[131.117.188.187] (helo/hostname mismatch)’

This is a reverse DNS error because the MTA host name of my Exchange system should be mail.ttlhosting.co.uk not remote.ttlhosting.co.uk 

How can I change this? 

Thanks

Dave