diff --git a/res/values/strings.xml b/res/values/strings.xml
index 9ece09ded0..ef4d7ed280 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -502,6 +502,9 @@
     <string name="MmsPreferencesFragment__manual_mms_settings_are_required">Manual MMS settings are required for your phone.</string>
     <string name="MmsPreferencesFragment__enabled">Enabled</string>
     <string name="MmsPreferencesFragment__disabled">Disabled</string>
+    <string name="MmsPreferencesFragment__not_set">Not set</string>
+    <string name="MmsPreferencesFragment__invalid_uri">The text entered was not a valid URI</string>
+    <string name="MmsPreferencesFragment__invalid_host">The text entered was not a valid host</string>
 
     <!-- prompt_passphrase_activity -->
     <string name="prompt_passphrase_activity__unlock">Unlock</string>
diff --git a/src/org/thoughtcrime/securesms/MmsPreferencesFragment.java b/src/org/thoughtcrime/securesms/MmsPreferencesFragment.java
index 489d273ea9..918e42b6dd 100644
--- a/src/org/thoughtcrime/securesms/MmsPreferencesFragment.java
+++ b/src/org/thoughtcrime/securesms/MmsPreferencesFragment.java
@@ -20,12 +20,17 @@ import android.content.Context;
 import android.os.Bundle;
 import android.preference.EditTextPreference;
 import android.preference.Preference;
+import android.preference.Preference.OnPreferenceChangeListener;
 import android.support.v4.preference.PreferenceFragment;
+import android.text.TextUtils;
 import android.widget.Toast;
 
 import org.thoughtcrime.securesms.mms.OutgoingMmsConnection;
 import org.thoughtcrime.securesms.util.TextSecurePreferences;
 
+import java.net.URI;
+import java.net.URISyntaxException;
+
 
 public class MmsPreferencesFragment extends PreferenceFragment {
 
@@ -47,22 +52,15 @@ public class MmsPreferencesFragment extends PreferenceFragment {
     } else {
       addPreferencesFromResource(R.xml.preferences_manual_mms);
     }
+    this.findPreference(TextSecurePreferences.MMSC_HOST_PREF).setOnPreferenceChangeListener(new ValidUriVerificationListener());
+    this.findPreference(TextSecurePreferences.MMSC_PROXY_HOST_PREF).setOnPreferenceChangeListener(new ValidHostnameVerificationListener());
+    this.findPreference(TextSecurePreferences.MMSC_PROXY_PORT_PREF).setOnPreferenceChangeListener(new EditTextVerificationListener());
+    this.findPreference(TextSecurePreferences.MMSC_USERNAME_PREF).setOnPreferenceChangeListener(new EditTextVerificationListener());
+    this.findPreference(TextSecurePreferences.MMSC_PASSWORD_PREF).setOnPreferenceChangeListener(new EditTextVerificationListener());
   }
 
   private void initializeEditTextSummary(final EditTextPreference preference) {
-    if (preference.getText() == null) {
-      preference.setSummary("Not set");
-    } else {
-      preference.setSummary(preference.getText());
-    }
-
-    preference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
-      @Override
-      public boolean onPreferenceChange(Preference pref, Object newValue) {
-        preference.setSummary(newValue == null ? "Not set" : ((String) newValue));
-        return true;
-      }
-    });
+    preference.setSummary(TextUtils.isEmpty(preference.getText()) ? getString(R.string.MmsPreferencesFragment__not_set) : preference.getText());
   }
 
   private void initializeEditTextSummaries() {
@@ -89,4 +87,57 @@ public class MmsPreferencesFragment extends PreferenceFragment {
 
     return context.getString(TextSecurePreferences.isUseLocalApnsEnabled(context) ? enabledResId : disabledResId);
   }
+
+  private class EditTextVerificationListener implements OnPreferenceChangeListener {
+    @Override
+    public boolean onPreferenceChange(Preference preference, Object newValue) {
+      String newString = (String)newValue;
+      if (isValid(newString)) {
+        preference.setSummary(TextUtils.isEmpty(newString) ? getString(R.string.MmsPreferencesFragment__not_set) : newString);
+        return true;
+      } else {
+        Toast.makeText(getActivity(), getErrorMessage(), Toast.LENGTH_LONG).show();
+        return false;
+      }
+    }
+
+    protected boolean isValid(String newString) { return true; }
+    protected int getErrorMessage() { return 0; }
+  }
+
+  private class ValidUriVerificationListener extends EditTextVerificationListener {
+    @Override
+    protected boolean isValid(String newString) {
+      if (TextUtils.isEmpty(newString)) return true;
+      try {
+        new URI(newString);
+        return true;
+      } catch (URISyntaxException mue) {
+        return false;
+      }
+    }
+
+    @Override
+    protected int getErrorMessage() {
+      return R.string.MmsPreferencesFragment__invalid_uri;
+    }
+  }
+
+  private class ValidHostnameVerificationListener extends EditTextVerificationListener {
+    @Override
+    protected boolean isValid(String newString) {
+      if (TextUtils.isEmpty(newString)) return true;
+      try {
+        URI uri = new URI(null, newString, null, null);
+        return true;
+      } catch (URISyntaxException mue) {
+        return false;
+      }
+    }
+
+    @Override
+    protected int getErrorMessage() {
+      return R.string.MmsPreferencesFragment__invalid_host;
+    }
+  }
 }
diff --git a/src/org/thoughtcrime/securesms/mms/OutgoingMmsConnection.java b/src/org/thoughtcrime/securesms/mms/OutgoingMmsConnection.java
index b509dceee3..66a892089d 100644
--- a/src/org/thoughtcrime/securesms/mms/OutgoingMmsConnection.java
+++ b/src/org/thoughtcrime/securesms/mms/OutgoingMmsConnection.java
@@ -47,16 +47,20 @@ public class OutgoingMmsConnection extends MmsConnection {
   protected HttpUriRequest constructRequest(boolean useProxy)
       throws IOException
   {
-    HttpPostHC4 request = new HttpPostHC4(apn.getMmsc());
-    request.addHeader("Accept", "*/*, application/vnd.wap.mms-message, application/vnd.wap.sic");
-    request.addHeader("x-wap-profile", "http://www.google.com/oha/rdf/ua-profile-kila.xml");
-    request.addHeader("Content-Type", "application/vnd.wap.mms-message");
-    request.setEntity(new ByteArrayEntityHC4(mms));
-    if (useProxy) {
-      HttpHost proxy = new HttpHost(apn.getProxy(), apn.getPort());
-      request.setConfig(RequestConfig.custom().setProxy(proxy).build());
+    try {
+      HttpPostHC4 request = new HttpPostHC4(apn.getMmsc());
+      request.addHeader("Accept", "*/*, application/vnd.wap.mms-message, application/vnd.wap.sic");
+      request.addHeader("x-wap-profile", "http://www.google.com/oha/rdf/ua-profile-kila.xml");
+      request.addHeader("Content-Type", "application/vnd.wap.mms-message");
+      request.setEntity(new ByteArrayEntityHC4(mms));
+      if (useProxy) {
+        HttpHost proxy = new HttpHost(apn.getProxy(), apn.getPort());
+        request.setConfig(RequestConfig.custom().setProxy(proxy).build());
+      }
+      return request;
+    } catch (IllegalArgumentException iae) {
+      throw new IOException(iae);
     }
-    return request;
   }
 
   public void sendNotificationReceived(boolean usingMmsRadio, boolean useProxyIfAvailable)