[exim] what chars in aliases?

Hi all

I would like to setup aliases such as
     8======D : a_unix_user
in /etc/aliases.

I mostly read the RFC about emails and (I think) I know the allowed
chars in an email adress.
What are the forbidden chars for the localparts in /etc/aliases?
The weird chars will only be the alias. The destination will be alphanum
string without weird things.

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