The identity's email address.

By default, the string must be 7-bit ASCII. If the text must contain any other characters, then you must use MIME encoded-word syntax (RFC 2047) instead of a literal string. MIME encoded-word syntax uses the following form:

CopyC#

=?charset?encoding?encoded-text?=

Note:
If you specify the CopyC# Source parameter, then bounce notifications and complaints will be sent to this email address. This takes precedence over any Return-Path header that you might include in the raw text of the message.