@JoJo: The problem with your question is that you make an unfair, possibly dangerous assumption:
The email header already includes the to and from.
The email header also includes the carbon copy field (CC) and may contain multiple "to" addressees.
The "from" field is not guaranteed to be accurate, especially when using personal accounts. The "from" field may include a nickname, pen name, business name, partial name, unfamiliar form of the name, etc. People are not always sure what name appears in the "from" field as that name is often configured once and then never seen again.
The "from" field also does not contain any alternate contact forms.
The recipient should not be confused by who the email is directed at (himself) and who it's coming from if the greeting and salutation are missing.
In larger organizations, it is common practice to copy managers on task-related e-mails. Especially with the CC field. This isn't done purely for show, it's also important for tracking and information sharing.
When I include two or more people on an e-mail it make perfect sense to address the target of that e-mail. If I send an e-mail to two co-workers and a manager, I may want only one worker to reply while everyone is involved.
Compare the following two:
#1:
from: me
to: boss, expert, peer
subject: a question
message: Hello expert;...
#2:
from: me
to: boss, expert, peer
subject: a question
message: Hello team;...
These are clearly different e-mails, as indicated by the first line of the message.
Are greetings and salutations redundant in an e-mail?
I think the above examples prove quite clearly that they are not redundant.