If you want to migrate to newer hardware, this is a plan of action which I successfully migrated previously.
Steps need to perform on old server:
1. Take full backup of /opt/zimbra folder(better compress it then it will not affect on file permission) and also backup /etc/hosts file.
Steps need to perform on new server:
1. Install same version of OS on new server(new server platform need to exactly be same version of old server including OS updates).
2. Install the same version of zimbra on new server(which need to exactly equal to old server zimbra version)
3. After installing zimbra server just stop all zimbra services and then backup and move /opt/zimbra folder to some where else.
4. Extract old server backup zimbra tar file and place it on corresponding locations(make sure to don't lose file permissions) and also make sure to configure same host name and fully configured name on /etc/hosts file.
5. start the zimbra service, if every thing done correctly service will up without any issue.
6. now its very simple just download latest zimbra version(what ever you are going zimbra version 8)
7. And then simply upgrade the zimbra version.
8. now all set you are successfully migrated.
Note: make sure to test the full scenario on test bid before performing on production environment.