                onMailFrom: function (address, session, callback) {
                    if (address.args && parseInt(address.args.SIZE, 10) > 50 * 1024) {
                        return callback(new Error('452 Insufficient channel storage: ' + address.address));
                    }

                    if (!/@valid.sender/.test(address.address)) {
                        return callback(new Error('Only user@valid.sender is allowed to send mail'));
                    }

                    if (address.args.SMTPUTF8) {
                        session.smtpUtf8 = true;
                    }

                    if (address.args.BODY === '8BITMIME') {
                        session.use8BitMime = true;
                    }

                    if (/[\x80-\uFFFF]/.test(address.address) && !session.smtpUtf8) {
                        return callback(new Error('Trying to use Unicode address without declaring SMTPUTF8 first'));
                    }

                    return callback(); // Accept the address
                },
The software constructs a string for a command to executed by a separate component
in another control sphere, but it does not properly delimit the
intended arguments, options, or switches within that command string.