Implementation for validating email addresses, it supports IDN domains and it checks if the domain has a mx record. It requires the xbill lib (http://www.xbill.org/dnsjava/).

MailChecker.java

/**
 * @copyright
 * This code is licensed under the Rekisoft Public License.
 * See http://www.rekisoft.eu/licenses/rkspl.html for more informations.
 */
package eu.rekisoft.android.util;

import java.net.IDN;
import java.util.Arrays;

import org.xbill.DNS.Lookup;
import org.xbill.DNS.MXRecord;
import org.xbill.DNS.Record;
import org.xbill.DNS.TextParseException;
import org.xbill.DNS.Type;

import android.annotation.TargetApi;
import android.os.Build;
import android.os.Build.VERSION_CODES;
import android.util.Log;

/**
 * Tool set for verifying email addressed on Android based on the DNS utils from xbill.
 * 
 * @author rekire
 * @version 0.8
 * @copyright This code is licensed under the Rekisoft Public License.<br/>
 *            See http://www.rekisoft.eu/licenses/rkspl.html for more informations.
 */
public final class MailChecker {
	/**
	 * The status of the mail address verification.
	 * 
	 * @author rekire
	 */
	public static enum AddressStatus {
		/** The address seems to be fine */
		valid,
		/** The address has some schema errors like a missing at sign */
		wrongSchema,
		/** The domain is currently not registed */
		notRegisted,
		/** The domain has no MX record (so the domain cannot receive mails) */
		noMxRecord,
		/** A typographic error was detected */
		typoDetected,
		/** The status of the address is unknown */
		unknown,
		/** The mail address check is pending */
		pending;

		private String mail;

		/**
		 * @return the suggested mail address.
		 */
		public String getMailAddress() {
			return mail;
		}

		/**
		 * Set the email address in case of a detected typo.
		 * 
		 * @param mail
		 *            The mail address which is guessed.
		 * @return this.
		 */
		protected AddressStatus setMailAddress(String mail) {
			this.mail = mail;
			return this;
		}

		/**
		 * @return <code>true</code> if the email address is not valid or a typo was detected.
		 */
		public boolean wrong() {
			return this != valid && this != typoDetected;
		}
	}
	
	/**
	 * A small list of well known email addresses.
	 */
	private static String[] domains = {"web.de", "gmx.de", "gmx.com", "gmx.net", "freenet.net", "hotmail.com", "gmail.com",
			"googlemail.com", "live.de", "live.com", "hotmail.de", "aol.com", "t-online.de", "hushmail.com", "uni.de", "yahoo.com",
			"yahoo.de"};

	static {
		// Set the network timeout to one second.
		Lookup.getDefaultResolver().setTimeout(1);
	}

	/**
	 * Let you set your own list of domains which you want to use for auto correction.
	 * 
	 * @param list
	 *            Your list of well known domains.
	 */
	public static void setDomainList(String[] list) {
		if(list != null) {
			domains = list;
		}
	}

	/**
	 * Checks if a mail address is correct and tries to correct it if possible.
	 * 
	 * @param mail
	 *            the input mail address.
	 * @return the status of the validation with a copy of the mail address on success.
	 */
	public static MailChecker.AddressStatus validate(String mail) {
		String domain = getDomain(mail);
		if(domain == null) {
			// System.err.println(mail + " is no valid email address");
			return AddressStatus.wrongSchema;
		}
		try {
			if(validateMxServer(domain)) {
				// System.out.println(mail + " is ok");
				return AddressStatus.valid.setMailAddress(mail);
			} else {
				for(String d : domains) {
					if(damerauLevenshteinDistance(d, domain, 128) <= 2) {
						// System.out.println(mail + " did you mean " + d + "?");
						return AddressStatus.typoDetected.setMailAddress(mail.substring(0, mail.indexOf("@") + 1) + d);
					}
				}
				if(doesDomainExists(domain)) {
					// System.err.println(mail + " has no mail servers");
					return AddressStatus.noMxRecord;
				} else {
					// System.err.println("Domain \"" + domain + "\" does not exists");
					return AddressStatus.notRegisted;
				}
			}
		} catch(IllegalStateException e) {
			return AddressStatus.unknown;
		}
	}
	
	/**
	 * Checks if a NS record exists for the given domain.
	 * 
	 * @param domain
	 *            the domain which should be checked.
	 * @return true if a NS record was found.
	 * @throws IllegalStateException
	 *             on network errors.
	 */
	private static boolean doesDomainExists(String domain) throws IllegalStateException {
		try {
			Lookup l = new Lookup(domain, Type.NS);
			Record[] result = l.run();
			if(l.getResult() == Lookup.TRY_AGAIN) {
				throw new IllegalStateException();
			}
			return result != null && result.length > 0;
		} catch(TextParseException e) {
		}
		return false;
	}

	/**
	 * Returns the domain portion of the mail address.
	 * 
	 * @param mail
	 *            the input mail address.
	 * @return <code>null</code> if the mail address is malformed or the domain.
	 */
	@TargetApi(Build.VERSION_CODES.GINGERBREAD)
	private static String getDomain(String mail) {
		String[] part = mail.split("@");
		if(part.length != 2) {
			Log.w(MailChecker.class.getSimpleName(), "Syntax error on " + mail);
			return null;
		}
		if(Build.VERSION.SDK_INT >= VERSION_CODES.GINGERBREAD) {
			return IDN.toASCII(part[1]);
		} else {
			Log.w(MailChecker.class.getSimpleName(), "No IDN support on this platform");
			return part[1];
		}
	}

	/**
	 * Checks if a MX record exists for the given domain.
	 * 
	 * @param domain
	 *            the domain which should be checked.
	 * @return true if a MX record was found.
	 * @throws IllegalStateException
	 *             on network errors.
	 */
	private static boolean validateMxServer(String domain) throws IllegalStateException {
		try {
			Lookup l = new Lookup(domain, Type.MX);
			Record[] result = l.run();
			if(l.getResult() == Lookup.TRY_AGAIN) {
				throw new IllegalStateException();
			}
			if(result != null && result.length > 0) {
				for(Record r : result) {
					MXRecord mx = (MXRecord)r;
					Record[] result2 = new Lookup(mx.getTarget(), Type.A).run();
					if(result2 != null && result2.length > 0) {
						// System.out.println("OK! MX: " + mx.getTarget() + " -> " + ((ARecord)result2[0]).getAddress().getHostAddress());
						return true;
					} else {
						// System.err.println("Fail: could not resolv " + mx.getTarget());
					}
				}
			}
		} catch(TextParseException e) {
			e.printStackTrace();
		}
		// System.err.println("Fail: not mx record for " + domain + " found");
		return false;
	}

	/**
	 * Calculated the Damerau-Levenshtein-Distance.
	 * 
	 * @param a
	 *            input string one.
	 * @param b
	 *            input string two.
	 * @param alphabetLength
	 *            the length of the alphabet.
	 * @return the distance.
	 * 
	 * @author M. Jessup (http://stackoverflow.com/a/6035519/995926)
	 */
	private static int damerauLevenshteinDistance(String a, String b, int alphabetLength) {
		final int INFINITY = a.length() + b.length();
		int[][] H = new int[a.length() + 2][b.length() + 2];
		H[0][0] = INFINITY;
		for(int i = 0; i <= a.length(); i++) {
			H[i + 1][1] = i;
			H[i + 1][0] = INFINITY;
		}
		for(int j = 0; j <= b.length(); j++) {
			H[1][j + 1] = j;
			H[0][j + 1] = INFINITY;
		}
		int[] DA = new int[alphabetLength];
		Arrays.fill(DA, 0);
		for(int i = 1; i <= a.length(); i++) {
			int DB = 0;
			for(int j = 1; j <= b.length(); j++) {
				int i1 = DA[b.charAt(j - 1)];
				int j1 = DB;
				int d = ((a.charAt(i - 1) == b.charAt(j - 1)) ? 0 : 1);
				if(d == 0)
					DB = j;
				H[i + 1][j + 1] = min(H[i][j] + d, H[i + 1][j] + 1, H[i][j + 1] + 1, H[i1][j1] + (i - i1 - 1) + 1 + (j - j1 - 1));
			}
			DA[a.charAt(i - 1)] = i;
		}
		return H[a.length() + 1][b.length() + 1];
	}

	/**
	 * Helper function for getting the minimal value of a set of ints.
	 * 
	 * @param nums
	 *            The integer values which should been checked.
	 * @return the minimal value.
	 */
	private static int min(int... nums) {
		int min = Integer.MAX_VALUE;
		for(int num : nums) {
			min = min < num ? min : num;
		}
		return min;
	}
}