Add an address to one of the recipient arrays or to the ReplyTo array. Because PHPMailer can’t validate addresses with an IDN without knowing the PHPMailer::$CharSet (that can still be modified after calling this function), addition of such addresses is delayed until send().
Addresses that have been added already return false, but do not throw exceptions.
(string) (Required) One of 'to', 'cc', 'bcc', or 'ReplyTo'
(string) (Required) The email address to send, resp. to reply to
(boolean) true on success, false if address already used or invalid in some way