diff --git a/src/com/fsck/k9/preferences/AccountSettings.java b/src/com/fsck/k9/preferences/AccountSettings.java
index 0a5142a81..8beeb7fa3 100644
--- a/src/com/fsck/k9/preferences/AccountSettings.java
+++ b/src/com/fsck/k9/preferences/AccountSettings.java
@@ -211,15 +211,19 @@ public class AccountSettings {
         UPGRADERS = Collections.unmodifiableMap(u);
     }
 
-    public static Map<String, String> validate(int version, Map<String, String> importedSettings,
+    public static Map<String, Object> validate(int version, Map<String, String> importedSettings,
             boolean useDefaultValues) {
         return Settings.validate(version, SETTINGS, importedSettings, useDefaultValues);
     }
 
-    public static Set<String> upgrade(int version, Map<String, String> validatedSettings) {
+    public static Set<String> upgrade(int version, Map<String, Object> validatedSettings) {
         return Settings.upgrade(version, UPGRADERS, SETTINGS, validatedSettings);
     }
 
+    public static Map<String, String> convert(Map<String, Object> settings) {
+        return Settings.convert(settings, SETTINGS);
+    }
+
     public static Map<String, String> getAccountSettings(SharedPreferences storage, String uuid) {
         Map<String, String> result = new HashMap<String, String>();
         String prefix = uuid + ".";
diff --git a/src/com/fsck/k9/preferences/FolderSettings.java b/src/com/fsck/k9/preferences/FolderSettings.java
index 88a050c14..6759a71ae 100644
--- a/src/com/fsck/k9/preferences/FolderSettings.java
+++ b/src/com/fsck/k9/preferences/FolderSettings.java
@@ -42,15 +42,19 @@ public class FolderSettings {
         UPGRADERS = Collections.unmodifiableMap(u);
     }
 
-    public static Map<String, String> validate(int version, Map<String, String> importedSettings,
+    public static Map<String, Object> validate(int version, Map<String, String> importedSettings,
             boolean useDefaultValues) {
         return Settings.validate(version, SETTINGS, importedSettings, useDefaultValues);
     }
 
-    public static Set<String> upgrade(int version, Map<String, String> validatedSettings) {
+    public static Set<String> upgrade(int version, Map<String, Object> validatedSettings) {
         return Settings.upgrade(version, UPGRADERS, SETTINGS, validatedSettings);
     }
 
+    public static Map<String, String> convert(Map<String, Object> settings) {
+        return Settings.convert(settings, SETTINGS);
+    }
+
     public static Map<String, String> getFolderSettings(SharedPreferences storage, String uuid,
             String folderName) {
         Map<String, String> result = new HashMap<String, String>();
diff --git a/src/com/fsck/k9/preferences/GlobalSettings.java b/src/com/fsck/k9/preferences/GlobalSettings.java
index 53c0f94f7..5dcae70bb 100644
--- a/src/com/fsck/k9/preferences/GlobalSettings.java
+++ b/src/com/fsck/k9/preferences/GlobalSettings.java
@@ -198,14 +198,18 @@ public class GlobalSettings {
         UPGRADERS = Collections.unmodifiableMap(u);
     }
 
-    public static Map<String, String> validate(int version, Map<String, String> importedSettings) {
+    public static Map<String, Object> validate(int version, Map<String, String> importedSettings) {
         return Settings.validate(version, SETTINGS, importedSettings, false);
     }
 
-    public static Set<String> upgrade(int version, Map<String, String> validatedSettings) {
+    public static Set<String> upgrade(int version, Map<String, Object> validatedSettings) {
         return Settings.upgrade(version, UPGRADERS, SETTINGS, validatedSettings);
     }
 
+    public static Map<String, String> convert(Map<String, Object> settings) {
+        return Settings.convert(settings, SETTINGS);
+    }
+
     public static Map<String, String> getGlobalSettings(SharedPreferences storage) {
         Map<String, String> result = new HashMap<String, String>();
         for (String key : SETTINGS.keySet()) {
diff --git a/src/com/fsck/k9/preferences/IdentitySettings.java b/src/com/fsck/k9/preferences/IdentitySettings.java
index 343972c66..f5ff270f5 100644
--- a/src/com/fsck/k9/preferences/IdentitySettings.java
+++ b/src/com/fsck/k9/preferences/IdentitySettings.java
@@ -38,15 +38,19 @@ public class IdentitySettings {
         UPGRADERS = Collections.unmodifiableMap(u);
     }
 
-    public static Map<String, String> validate(int version, Map<String, String> importedSettings,
+    public static Map<String, Object> validate(int version, Map<String, String> importedSettings,
             boolean useDefaultValues) {
         return Settings.validate(version, SETTINGS, importedSettings, useDefaultValues);
     }
 
-    public static Set<String> upgrade(int version, Map<String, String> validatedSettings) {
+    public static Set<String> upgrade(int version, Map<String, Object> validatedSettings) {
         return Settings.upgrade(version, UPGRADERS, SETTINGS, validatedSettings);
     }
 
+    public static Map<String, String> convert(Map<String, Object> settings) {
+        return Settings.convert(settings, SETTINGS);
+    }
+
     public static Map<String, String> getIdentitySettings(SharedPreferences storage, String uuid,
             int identityIndex) {
         Map<String, String> result = new HashMap<String, String>();
@@ -104,6 +108,11 @@ public class IdentitySettings {
             return value;
         }
 
+        @Override
+        public String toString(Object value) {
+            return (value != null) ? value.toString() : null;
+        }
+
         @Override
         public String toPrettyString(Object value) {
             return (value == null) ? "" : value.toString();
diff --git a/src/com/fsck/k9/preferences/Settings.java b/src/com/fsck/k9/preferences/Settings.java
index 6619b84a6..207c63464 100644
--- a/src/com/fsck/k9/preferences/Settings.java
+++ b/src/com/fsck/k9/preferences/Settings.java
@@ -36,11 +36,11 @@ public class Settings {
      */
     public static final int VERSION = 3;
 
-    public static Map<String, String> validate(int version, Map<String,
+    public static Map<String, Object> validate(int version, Map<String,
             TreeMap<Integer, SettingsDescription>> settings,
             Map<String, String> importedSettings, boolean useDefaultValues) {
 
-        Map<String, String> validatedSettings = new HashMap<String, String>();
+        Map<String, Object> validatedSettings = new HashMap<String, Object>();
         for (Map.Entry<String, TreeMap<Integer, SettingsDescription>> versionedSetting :
                 settings.entrySet()) {
 
@@ -63,8 +63,7 @@ public class Settings {
                 String prettyValue = importedSettings.get(key);
                 try {
                     Object internalValue = desc.fromPrettyString(prettyValue);
-                    String importedValue = desc.toString(internalValue);
-                    validatedSettings.put(key, importedValue);
+                    validatedSettings.put(key, internalValue);
                     useDefaultValue = false;
                 } catch (InvalidSettingValueException e) {
                     Log.v(K9.LOG_TAG, "Key \"" + key + "\" has invalid value \"" + prettyValue +
@@ -76,8 +75,7 @@ public class Settings {
 
             if (useDefaultValue) {
                 Object defaultValue = desc.getDefaultValue();
-                String value = (defaultValue != null) ? desc.toString(defaultValue) : null;
-                validatedSettings.put(key, value);
+                validatedSettings.put(key, defaultValue);
             }
         }
 
@@ -103,9 +101,9 @@ public class Settings {
      */
     public static Set<String> upgrade(int version, Map<Integer, SettingsUpgrader> upgraders,
             Map<String, TreeMap<Integer, SettingsDescription>> settings,
-            Map<String, String> validatedSettings) {
+            Map<String, Object> validatedSettings) {
 
-        Map<String, String> upgradedSettings = validatedSettings;
+        Map<String, Object> upgradedSettings = validatedSettings;
         Set<String> deletedSettings = null;
 
         for (int toVersion = version + 1; toVersion <= VERSION; toVersion++) {
@@ -131,7 +129,7 @@ public class Settings {
                         // Insert default value to upgradedSettings
                         SettingsDescription setting = versionedSettings.firstEntry().getValue();
                         Object defaultValue = setting.getDefaultValue();
-                        upgradedSettings.put(settingName, setting.toString(defaultValue));
+                        upgradedSettings.put(settingName, defaultValue);
 
                         if (K9.DEBUG) {
                             String prettyValue = setting.toPrettyString(defaultValue);
@@ -160,6 +158,45 @@ public class Settings {
         return deletedSettings;
     }
 
+    /**
+     * Convert settings from the internal representation to the string representation used in the
+     * preference storage.
+     *
+     * @param settings
+     *         The map of settings to convert.
+     * @param settingDescriptions
+     *         The structure containing the {@link SettingsDescription} objects that will be used
+     *         to convert the setting values.
+     *
+     * @return The settings converted to the string representation used in the preference storage.
+     */
+    public static Map<String, String> convert(Map<String, Object> settings,
+            Map<String, TreeMap<Integer, SettingsDescription>> settingDescriptions) {
+
+        Map<String, String> serializedSettings = new HashMap<String, String>();
+
+        for (Entry<String, Object> setting : settings.entrySet()) {
+            String settingName = setting.getKey();
+            Object internalValue = setting.getValue();
+
+            SettingsDescription settingDesc =
+                settingDescriptions.get(settingName).lastEntry().getValue();
+
+            if (settingDesc != null) {
+                String stringValue = settingDesc.toString(internalValue);
+
+                serializedSettings.put(settingName, stringValue);
+            } else {
+                if (K9.DEBUG) {
+                    Log.w(K9.LOG_TAG, "Settings.serialize() called with a setting that should " +
+                            "have been removed: " + settingName);
+                }
+            }
+        }
+
+        return serializedSettings;
+    }
+
     /**
      * Creates a {@link TreeMap} linking version numbers to {@link SettingsDescription} instances.
      *
@@ -327,7 +364,7 @@ public class Settings {
          * @return A set of setting names that were removed during the upgrade process or
          *         {@code null} if none were removed.
          */
-        public Set<String> upgrade(Map<String, String> settings);
+        public Set<String> upgrade(Map<String, Object> settings);
     }
 
 
diff --git a/src/com/fsck/k9/preferences/SettingsImporter.java b/src/com/fsck/k9/preferences/SettingsImporter.java
index bfaa1a996..aa307ba66 100644
--- a/src/com/fsck/k9/preferences/SettingsImporter.java
+++ b/src/com/fsck/k9/preferences/SettingsImporter.java
@@ -304,7 +304,7 @@ public class SettingsImporter {
             SharedPreferences.Editor editor, int contentVersion, ImportedSettings settings) {
 
         // Validate global settings
-        Map<String, String> validatedSettings = GlobalSettings.validate(contentVersion,
+        Map<String, Object> validatedSettings = GlobalSettings.validate(contentVersion,
                 settings.settings);
 
         // Upgrade global settings to current content version
@@ -312,11 +312,14 @@ public class SettingsImporter {
             GlobalSettings.upgrade(contentVersion, validatedSettings);
         }
 
+        // Convert global settings to the string representation used in preference storage
+        Map<String, String> stringSettings = GlobalSettings.convert(validatedSettings);
+
         // Use current global settings as base and overwrite with validated settings read from the
         // import file.
         Map<String, String> mergedSettings =
             new HashMap<String, String>(GlobalSettings.getGlobalSettings(storage));
-        mergedSettings.putAll(validatedSettings);
+        mergedSettings.putAll(stringSettings);
 
         for (Map.Entry<String, String> setting : mergedSettings.entrySet()) {
             String key = setting.getKey();
@@ -398,7 +401,7 @@ public class SettingsImporter {
         }
 
         // Validate account settings
-        Map<String, String> validatedSettings =
+        Map<String, Object> validatedSettings =
             AccountSettings.validate(contentVersion, account.settings.settings,
                     !mergeImportedAccount);
 
@@ -407,14 +410,17 @@ public class SettingsImporter {
             AccountSettings.upgrade(contentVersion, validatedSettings);
         }
 
+        // Convert account settings to the string representation used in preference storage
+        Map<String, String> stringSettings = AccountSettings.convert(validatedSettings);
+
         // Merge account settings if necessary
         Map<String, String> writeSettings;
         if (mergeImportedAccount) {
             writeSettings = new HashMap<String, String>(
                     AccountSettings.getAccountSettings(prefs.getPreferences(), uuid));
-            writeSettings.putAll(validatedSettings);
+            writeSettings.putAll(stringSettings);
         } else {
-            writeSettings = validatedSettings;
+            writeSettings = stringSettings;
         }
 
         // Write account settings
@@ -456,7 +462,7 @@ public class SettingsImporter {
             String uuid, ImportedFolder folder, boolean overwrite, Preferences prefs) {
 
         // Validate folder settings
-        Map<String, String> validatedSettings =
+        Map<String, Object> validatedSettings =
             FolderSettings.validate(contentVersion, folder.settings.settings, !overwrite);
 
         // Upgrade folder settings to current content version
@@ -464,14 +470,17 @@ public class SettingsImporter {
             FolderSettings.upgrade(contentVersion, validatedSettings);
         }
 
+        // Convert folder settings to the string representation used in preference storage
+        Map<String, String> stringSettings = FolderSettings.convert(validatedSettings);
+
         // Merge folder settings if necessary
         Map<String, String> writeSettings;
         if (overwrite) {
             writeSettings = FolderSettings.getFolderSettings(prefs.getPreferences(),
                     uuid, folder.name);
-            writeSettings.putAll(validatedSettings);
+            writeSettings.putAll(stringSettings);
         } else {
-            writeSettings = validatedSettings;
+            writeSettings = stringSettings;
         }
 
         // Write folder settings
@@ -550,7 +559,7 @@ public class SettingsImporter {
 
             if (identity.settings != null) {
                 // Validate identity settings
-                Map<String, String> validatedSettings = IdentitySettings.validate(
+                Map<String, Object> validatedSettings = IdentitySettings.validate(
                         contentVersion, identity.settings.settings, !mergeSettings);
 
                 // Upgrade identity settings to current content version
@@ -558,14 +567,17 @@ public class SettingsImporter {
                     IdentitySettings.upgrade(contentVersion, validatedSettings);
                 }
 
+                // Convert identity settings to the representation used in preference storage
+                Map<String, String> stringSettings = IdentitySettings.convert(validatedSettings);
+
                 // Merge identity settings if necessary
                 Map<String, String> writeSettings;
                 if (mergeSettings) {
                     writeSettings = new HashMap<String, String>(IdentitySettings.getIdentitySettings(
                             prefs.getPreferences(), uuid, writeIdentityIndex));
-                    writeSettings.putAll(validatedSettings);
+                    writeSettings.putAll(stringSettings);
                 } else {
-                    writeSettings = validatedSettings;
+                    writeSettings = stringSettings;
                 }
 
                 // Write identity settings