No.
By convention, e-mail names are treated as case-insensitive.
However, per RFC 2181:
http://www.ietf.org/rfc/rfc2821.txt
The local-part of a mailbox MUST BE treated as case sensitive.
Therefore, SMTP implementations MUST take care to preserve the case of
mailbox local-parts. Mailbox domains are not case sensitive. In
particular, for some hosts the user "smith" is different from the user
"Smith". However, exploiting the case sensitivity of mailbox
local-parts impedes interoperability and is discouraged.
