my $_tsub = "SendMultiPartMemberEmailMimeLiteSendGrid";
    if(exists &{$_tsub}) {
        # code to call it
    } else {
        require "/path/to/the/file/SendMultiPartMemberEmailMimeLiteSendGrid.pl";
        # code to call it
    }

##</code><code>##

    my $_tsub = "SendMultiPartMemberEmailMimeLiteSendGrid";
    if ( not exists &{$_tsub} ) {
        require "/path/to/the/file/SendMultiPartMemberEmailMimeLiteSendGrid.pl";
    }
    # code to call it

##</code><code>##

    require "/path/to/the/file/SendMultiPartMemberEmailMimeLiteSendGrid.pl";
    # code to call it