Java mail IMAP list example - List all the email addresses in an IMAP mailbox

By Alvin Alexander. Last updated: March 12, 2018

Java Mail (JavaMail) IMAP FAQ: Can you show me how to get a list of all the email addresses in an IMAP mailbox using the Java Mail API (JavaMail API)?

Sure. Here's the source code for a Java mail (JavaMail) program that extracts all of the "from" fields out of a specified mailbox. This works for both POP3 and IMAP mailboxes.

Before going to the code, note the cool use of a TreeSet (java.util.TreeSet) in this example. Based on our offline discussion, you mentioned that you really want is this:

Only the unique email addresses, and
The addresses sorted alphabetically.

Therefore, a TreeSet is a great data type for this purpose.

My JavaMail IMAP email address list program

With no further ado, here is the source code for my JavaMail email address list/extractor:

import javax.mail.*;
import javax.mail.internet.*;
import java.util.*;
import java.io.*;

/**
 * My JavaMail email address extractor.
 * A JavaMail API example.
 * @author alvin alexander, alvinalexander.com.
 */
public class AddressExtractor
{

  public static void main(String[] args)
  {
    Properties props = new Properties();

    String host      = args[0];
    String username  = args[1];
    String password  = args[2];
    //String provider  = "pop3";
    String provider  = "imap";

    try
    {
      //Connect to the server
      Session session = Session.getDefaultInstance(props, null);
      Store store     = session.getStore(provider);
      store.connect(host, username, password);

      //open the inbox folder
      Folder inbox = store.getFolder("INBOX");
      inbox.open(Folder.READ_ONLY);

      // get a list of javamail messages as an array of messages
      Message[] messages = inbox.getMessages();

      TreeSet treeSet = new TreeSet();

      for(int i = 0; i < messages.length; i++)
      {
        String from = getFrom(messages[i]);
        if ( from!=null)
        {
          from = removeQuotes(from);
          treeSet.add(from);
        }
      }

      Iterator it = treeSet.iterator();
      while ( it.hasNext() )
      {
        System.out.println("from: " + it.next());
      }

      //close the inbox folder but do not
      //remove the messages from the server
      inbox.close(false);
      store.close();
    }
    catch (NoSuchProviderException nspe)
    {
      System.err.println("invalid provider name");
    }
    catch (MessagingException me)
    {
      System.err.println("messaging exception");
      me.printStackTrace();
    }
  }

  private static String getFrom(Message javaMailMessage) 
  throws MessagingException
  {
    String from = "";
    Address a[] = javaMailMessage.getFrom();
    if ( a==null ) return null;
    for ( int i=0; i<a.length; i++ )
    {
      Address address = a[i];
      from = from + address.toString();
    }

    return from;
  }

  private static String removeQuotes(String stringToModify)
  {
    int indexOfFind = stringToModify.indexOf(stringToModify);
    if ( indexOfFind < 0 ) return stringToModify;

    StringBuffer oldStringBuffer = new StringBuffer(stringToModify);
    StringBuffer newStringBuffer = new StringBuffer();
    for ( int i=0, length=oldStringBuffer.length(); i<length; i++ )
    {
      char c = oldStringBuffer.charAt(i);
      if ( c == '"' || c == '\'' )
      {
        // do nothing
      }
      else
      {
        newStringBuffer.append(c);
      }

    }
    return new String(newStringBuffer);
  }

}

JavaMail IMAP list example - Discussion

Besides the TreeSet and JavaMail stuff going on, the removeQuotes() method may also be of interest to you. This method removes single- and double-quotes from the email address. During testing, I ran into situations where one email address was *almost* the same as another address, except for cases where one email address had a name embedded in single-quotes, and the other address had no quotes or double-quotes. Because both addresses are technically the same for what I needed, I added this method to strip out all quotes.

Note that you will also need the following JavaMail API jar files for this Java email extractor class to work: