Re: Fortimail Firmware Upgrade
In a case like this, you want to look at the 6.0.5 release notes and confirm what's required to get you there. The 6.0.5 release notes confirm that anything higher than 5.4.6 is OK to directly upgrade to 6.0.5
So you should be able to go 6.0.2 -> 6.0.5 -> 6.2.4 (build 272) > 6.4.0 (build 384).
Though now since 6.4.1 is out you can do this instead: (Confirmed in the 6.4.1 release notes)
6.0.2 -> 6.0.5 -> 6.2.4 (build 272) > 6.4.1 (build 414 )
As a general rule you NEVER want to downgrade. Best case you're in an unsupported configuration, worst case you end up loosing your configuration or creating a security vulnerability.
The release notes say " Firmware downgrading is not recommended and not supported in general.", and then proceed to tell you that if you really want to do it, you need to do a factory reset first anyway...