Develop Reference

How To Detect An Email Address Is Real

IMPORTANT
I have been blocked by hotmail services. There is a control mechanism
called spamhaus which kicked me out. I'm stuck right now.
I am trying to detect an email address is valid and if its valid then check if this email address potentially used (I know that its not certain). For example, lets assume that there is a website with domain myimaginarydomain.com. If I run code below, I guess it won't fail because domain address is valid. But nobody can take an email address with that domain.
Is there any way to find out that email address is valid? (In this case its invalid)
I don't want to send confirmation email
Sending ping may be useful?
public class Application {
private static EmailValidator validator = EmailValidator.getInstance();
public static void main(String[] args) {
while (true) {
Scanner scn = new Scanner(System.in);
String email = scn.nextLine();
boolean isValid = validateEmail(email);
System.out.println("Syntax is : " + isValid);
if (isValid) {
String domain = email.split("#")[1];
try {
int test = doLookup(domain);
System.out.println(domain + " has " + test + " mail servers");
} catch (NamingException e) {
System.out.println(domain + " has 0 mail servers");
}
}
}
}
private static boolean validateEmail(String email) {
return validator.isValid(email);
}
static int doLookup(String hostName) throws NamingException {
Hashtable env = new Hashtable();
env.put("java.naming.factory.initial",
"com.sun.jndi.dns.DnsContextFactory");
DirContext ictx = new InitialDirContext(env);
Attributes attrs =
ictx.getAttributes(hostName, new String[]{"MX"});
Attribute attr = attrs.get("MX");
if (attr == null) return (0);
return (attr.size());
}
}

There is no failsafe way to do this in all cases, but, assuming the server uses SMTP then https://www.labnol.org/software/verify-email-address/18220/ gives quite a good tutorial on one method that may work.
The method used in the tutorial relies on OS tools, so you will need to ensure they exist before using them. a ProcessBuilder may help. Alternatively, you can open a socket directly in code and avoid using OS-dependent tools.
Essentially, you find out what the mail servers are (using nslookup), then telnet to one of the mail servers and start writing an email:
3a: Connect to the mail server:
telnet gmail-smtp-in.l.google.com 25
3b: Say hello to the other server
HELO
3c: Identify yourself with some fictitious email address
mail from:<labnol#labnol.org>
3d: Type the recipient’s email address that you are trying to verify:
rcpt to:<billgates#gmail.com>
The server response for rcpt to command will give you an idea whether an email address is valid or not. You’ll get an “OK” if the address exists else a 550 error

There really is no sensible way except trying to send a notification with a token to the address and ask the other party to confirm it, usually by visiting a web-page:
the recipients MX may be unavailable at the moment but come back online later, so you cannot rely on a lookup in real time;
just because the MX accepts the email doesn't mean that the address is valid, the message could bounce later down the pipe (think UUCP);
if this is some kind of registration service, you need to provide some confirmation step anyway as otherwise it'd become too easy to subscribe random strangers on the internet that do not want your service.

Odd InetAddress.isReachable() issue

My work is developing software for network capable cameras for retail enviroments. One of the peices of software my team is developing is a webserver that retrieves various reports generated in HTML by the camera itself (which has its own embedded webserver) and stored on the camera. Our software will then GET these reports from the camera and store it on a central webserver.
While we are fine plugging in the IPs of the cameras into our software, I am developing a simple Java class that will query the network and locate all cameras on the network.
The problem though is that while it runs just fine on my PC, and my coworker's PC, when we attempt to run it on the actual webserver PC that will host our software... it runs, but says every IP in the subnet is offline / unreachable EXCEPT for the gateway IP.
For example, if I run it from my PC or my coworkers PC when plugged into the closed LAN, I get the following active IPs found along with a flag telling me if its a camera or not.
(gateway is 192.168.0.1, subnet mask is 255.255.255.0, which means full range of 256 devices to be looked for)
IP:/192.168.0.1 Active:true Camera:false
IP:/192.168.0.100 Active:true Camera:true <- this is camera 1
IP:/192.168.0.101 Active:true Camera:true <- this is camera 2
IP:/192.168.0.103 Active:true Camera:false <- my PC
IP:/192.168.0.104 Active:true Camera:false <- this is our webserver
But for some reason, when running the same program from the webserver PC, using the same JRE, I only get the following found
IP:/192.168.0.1 Active:true Camera:false
Now my code, instead of enumerating through each IP in order on the main Thread, instead creates a seperate Thread for each IP to be checked and runs them concurrently (else it would take little over 21 minutes to enumerate through the entire IP range at a timeout of 5000ms / IP). The main Thread then re-runs these IP scan threads every 15 seconds over and over.
I have checked that all the threads are running to completion on all the PCs, no exceptions are being thrown. Even verified that none of the threads are getting stuck. Each Thread takes about 5001 to 5050ms from start to complete, and those Threads that have an active IP finish sooner (>5000ms), so I know that its correctly waiting the full 5000ms in the ipAddr.isReachable(5000) method.
Me and my coworker are stumped at this point while it seems to reach those active IPs fine when run on our PCs, yet getting no response from the webserver PC???
We have ruled out firewall issues, admin access issues, etc.. The only difference is that our webserver is Embedded Win XP, and our PCs are Windows 7.
This has us stumped. Any ideas why?
Below is the code that is running each IP Thread:
public void CheckIP() {
new Thread() {
#Override
public void run() {
try {
isActive = ipAddr.isReachable(5000);
if (isActive) {
if (!isCamera) {
isCamera = new IpHttpManager().GetResponse(ipAddr.toString());
}
} else {
isCamera = false;
}
} catch (Exception e) {
e.printStackTrace();
}
}
}.start();
}
EDIT: Here is the code that builds each IP to check after determining the range based on gateway and subnet...
for(int i=subMin; i<=subMax; i++) {
byte[] ip = new byte[] {(byte)oct[0],(byte)oct[1],(byte)oct[2],(byte)i};
try {
scanners[subCount] = new IpScan(InetAddress.getByAddress(ip));
subCount++;
} catch (UnknownHostException e) {
e.printStackTrace();
}}

Thanks everyone, but I never did figure out or pinpoint why this oddity was happening. Everything I checked for was not the cause, so this question can be closed.
In any case, I ended up working around it completely. Instead of using InetAddress, I just went native and built my own ICMP ping class instead, via JNA, invoking Windows libraries IPHLPAPI.DLL and WSOCK32.DLL. Here is what I used...
public interface InetAddr extends StdCallLibrary {
InetAddr INSTANCE = (InetAddr)
Native.loadLibrary("wsock32.dll", InetAddr.class);
ULONG inet_addr(String cp); //in_addr creator. Creates the in_addr C struct used below
}
public interface IcmpEcho extends StdCallLibrary {
IcmpEcho INSTANCE = (IcmpEcho)
Native.loadLibrary("iphlpapi.dll", IcmpEcho.class);
int IcmpSendEcho(
HANDLE IcmpHandle, //Handle to the ICMP
ULONG DestinationAddress, //Destination address, in the form of an in_addr C Struct defaulted to ULONG
Pointer RequestData, //Pointer to the buffer where my Message to be sent is
short RequestSize, //size of the above buffer. sizeof(Message)
byte[] RequestOptions, //OPTIONAL!! Can set this to NULL
Pointer ReplyBuffer, //Pointer to the buffer where the replied echo is written to
int ReplySize, //size of the above buffer. Normally its set to the sizeof(ICMP_ECHO_REPLY), but arbitrarily set it to 256 bytes
int Timeout); //time, as int, for timeout
HANDLE IcmpCreateFile(); //win32 ICMP Handle creator
boolean IcmpCloseHandle(HANDLE IcmpHandle); //win32 ICMP Handle destroyer
}
And then using those to create the following method...
public void SendReply(String ipAddress) {
final IcmpEcho icmpecho = IcmpEcho.INSTANCE;
final InetAddr inetAddr = InetAddr.INSTANCE;
HANDLE icmpHandle = icmpecho.IcmpCreateFile();
byte[] message = new String("thisIsMyMessage!".toCharArray()).getBytes();
Memory messageData = new Memory(32); //In C/C++ this would be: void *messageData = (void*) malloc(message.length);
messageData.write(0, message, 0, message.length); //but ignored the length and set it to 32 bytes instead for now
Pointer requestData = messageData;
Pointer replyBuffer = new Memory(256);
replyBuffer.clear(256);
// HERE IS THE NATIVE CALL!!
reply = icmpecho.IcmpSendEcho(icmpHandle,
inetAddr.inet_addr(ipAddress),
requestData,
(short) 32,
null,
replyBuffer,
256,
timeout);
// NATIVE CALL DONE, CHECK REPLY!!
icmpecho.IcmpCloseHandle(icmpHandle);
}
public boolean IsReachable () {
return (reply > 0);
}

My guess is that your iteration logic to determine the different ip address is based upon different configuration hence your pc's fetches all addresses but your webserver doesn't.
Try adding debug in the logic where you build up the list of ip adresses to check.

Identify server on Tomcat (HttpServletRequest.getLocalAddr() fails)

With Tomcat setup behind Apache, how can an id (IP address ideally) of the server be easily determined?
The specific situation is that multiple servers are setup behind a load balancer, thus the incoming request host name is non-unique and insufficient to identify a particular server for logging purposes. Using HttpServletRequest.getLocalAddr() is unfortunately returning the same hostname instead of the IP address as would be expected (I am assuming this is related to this very old issue here: https://issues.apache.org/bugzilla/show_bug.cgi?id=46082).
Is there a way to make getLocalAddr() perform as documented, or are other methods required to query the IP address of the server?

On our project, we use JMX to get all the config information.
It takes a few steps, because it is like navigating down the server.xml file
This link has some info: http://oss.wxnet.org/mbeans.html
It is probably overkill if all you want is the IP, but I thought I'd throw it out there.
MBeanServer mbeanServer = ManagementFactory.getPlatformMBeanServer();
Set<ObjectName> theConnectors = mbeanServer.queryNames(
new ObjectName("Catalina:type=Connector,*"),
null);
if (theConnectors != null)
{
for (ObjectName nextConnectorName : theConnectors)
{
InetAddress theInetAddress = (InetAddress) mbeanServer.getAttribute(
nextConnectorName,
"address");
if (theInetAddress != null)
{
ipAddress = theInetAddress.getHostAddress();
}
if (!StringUtil.isEmpty(ipAddress))
{
// found the IP address
break;
}
}
}

For my situation, the solution was to get the IP address of the server directly instead of attempting to get the local address via HttpServleRequest.
I cached the IP for use in my filter via:
private static final String serverIp;
static {
String addressString = null;
try
{
InetAddress address = InetAddress.getLocalHost();
addressString = address.getHostAddress();
} catch (Exception e)
{
logger.error("Exception while attempting to determine local ip address",e);
}
if (addressString != null) serverIp = addressString;
else serverIp = "unknown";
}

I had a similar issue recently (a few years after the original question) and found this question and answers. The issue in my case was that the ServletRequest#getLocalAddr() implementation was returning the remote address instead of the local address. The issue was caused by a regression in Tomcat v9.0.22. It was fixed in v9.0.23. See the question and answer here:
https://stackoverflow.com/a/57725039/9602527

Function hangs? on packet.setAddress()

Ok so the program is designed to take in connections, validate them, and resend that validation code. Before anyone get's angry it's just a simple little project and is not designed to be overly complex haha. However for some very strange reason the function is hanging on send.setAddess(packet.getAddress); I know this because I have commented out each individual line of code that deals with the Datagram packet "send" and have found that it "hangs" (or never progresses forward in the method again) on that particular line. Any thoughts? Am I doing something cluelessly wrong? I tried it on a linux server as well to make sure it didn't have anything to do with me and the same crap happened.
public static boolean authorize(String n, DatagramPacket packet) {
DatagramPacket send = new DatagramPacket(new byte[4096], 4096);
try {
System.out.println("in auth");
String[] t1 = n.split("%#");
String name = t1[1];
int k = genKey(name);
clients.put(name, k);
send.setAddress(packet.getAddress());
System.out.println("set add");
send.setPort(packet.getPort());
System.out.println("set port");
send.setData(("l-succeed%#" + Integer.toString(k)).getBytes());
System.out.println("set data");
main.dispathcer(send);
System.out.println("called send");
return true;
} catch(Exception e) {
send.setData("l-failed".getBytes());
main.dispathcer(send);
return false;
}
}
EDIT: it took 6 minutes before the authorization token was received by the client. So obviously the setAddress() works but is taking far too long...

It's possible that the process is hanging because there's an issue doing DNS resolution on the address for packet when you call .getAddress(). A few DNS calls are made in order to create the InetAddress object. On these machines, are you able to do a reverse DNS lookup on the IP that the packet packet came from? Try setting an entry for this IP in your /etc/hosts file.

Someone knows a mail (SMTP) delivery library for Java?

I'd like to send mail without bothering with the SMTP-Server which is used for delivery.
So JavaMail API doesn't work for me because I have to specify a SMTP server to connect to.
I'd like the library to find out on its own which SMTP server is responsible for which email address by querying the MX record of the mail address domain.
I'm looking for something like Aspirin. Unfortunately I can't use Aspirin itself because the development stopped 2004 and the library fails to communicate with modern spam hardened servers correctly.
An embeddable version of James would do the task. But I haven't found documentation concerning whether this is possible.
Or does anyone know about other libraries I could use?

One possible solution: get the MX record on your own and use JavaMail API.
You can get the MX record using the dnsjava project:
Maven2 dependency:
<dependency>
<groupId>dnsjava</groupId>
<artifactId>dnsjava</artifactId>
<version>2.0.1</version>
</dependency>
Method for MX record retrieval:
public static String getMXRecordsForEmailAddress(String eMailAddress) {
String returnValue = null;
try {
String hostName = getHostNameFromEmailAddress(eMailAddress);
Record[] records = new Lookup(hostName, Type.MX).run();
if (records == null) { throw new RuntimeException("No MX records found for domain " + hostName + "."); }
if (log.isTraceEnabled()) {
// log found entries for debugging purposes
for (int i = 0; i < records.length; i++) {
MXRecord mx = (MXRecord) records[i];
String targetString = mx.getTarget().toString();
log.trace("MX-Record for '" + hostName + "':" + targetString);
}
}
// return first entry (not the best solution)
if (records.length > 0) {
MXRecord mx = (MXRecord) records[0];
returnValue = mx.getTarget().toString();
}
} catch (TextParseException e) {
throw new RuntimeException(e);
}
if (log.isTraceEnabled()) {
log.trace("Using: " + returnValue);
}
return returnValue;
}
private static String getHostNameFromEmailAddress(String mailAddress) throws TextParseException {
String parts[] = mailAddress.split("#");
if (parts.length != 2) throw new TextParseException("Cannot parse E-Mail-Address: '" + mailAddress + "'");
return parts[1];
}
Sending mail via JavaMail code:
public static void sendMail(String toAddress, String fromAddress, String subject, String body) throws AddressException, MessagingException {
String smtpServer = getMXRecordsForEmailAddress(toAddress);
// create session
Properties props = new Properties();
props.put("mail.smtp.host", smtpServer);
Session session = Session.getDefaultInstance(props);
// create message
Message msg = new MimeMessage(session);
msg.setFrom(new InternetAddress(fromAddress));
msg.setRecipient(Message.RecipientType.TO, new InternetAddress(toAddress));
msg.setSubject(subject);
msg.setText(body);
// send message
Transport.send(msg);
}

This is completely the wrong way to handle this.
Anyone connected to the internet will have some kind of "legit" SMTP server available to them to take the submission of email -- your ISP, your office, etc.
You WANT to leverage because they do several things for you.
1) they take your message and the responsibility to handle that message. After you drop it off, it's not your problem anymore.
2) Any mail de-spamming technologies are handled by the server. Even better, when/if those technologies change (Domain keys anyone?), the server handles it, not your code.
3) You, as a client of that sending mail system, already have whatever credentials you need to talk to that server. Main SMTP servers are locked down via authentication, IP range, etc.
4) You're not reinventing the wheel. Leverage the infrastructure you have. Are you writing an application or a mail server? Setting up mail server is an every day task that is typically simple to do. All of those casual "dumb" users on the internet have managed to get email set up.

Don't.
Sending email is much more complex than it seems. Email servers excel at (or should excel at) reliable delivery.
Set up a separate email server if you need to- that will be essentially the same as implementing one in Java (I doubt you will find libraries for this task- they would be essentially complete mail servers), but much more simpler.