Pffff... Disclaimers on emails are to all intents and purposes worthless from a legal perspective. They're only useful to notify recipients where they should re-send document if recieved in error.
Email is simply a medium; what is important is the content and an organisation should ascribe the same value to a particular type of content regardless of content.
Now, there could be an issue about legal admissibility, which arises where it is not always possible to prove that a document contains an unaltered version of the content. If you can't then a judge would be entitled to refuse to accept a document into proceedings.
Without more detail about precisely you want to know, it's difficult to give an exact answer.