private String constructTcpInfo(final InetAddress host) {
        // if it is not successful it just returns the address
        final String domain = host.getCanonicalHostName();
        final String address = host.getHostAddress();
        // check whether the host name resolution was successful
        if (domain.equals(address)) {
            return "[" + address + "]";
        }
        return domain + " [" + address + "]";
    }
Returns a formatted TCP-info element, depending on the success of the IP
address name resolution either with domain name or only the address literal.

@param host the address of the remote SMTP client.
@return the formatted TCP-info element as defined by RFC 5321
src/main/java/de/gessnerfl/fakesmtp/smtp/io/ReceivedHeaderStream.java