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diff --git a/java/com/google/gerrit/server/account/Emails.java b/java/com/google/gerrit/server/account/Emails.java
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+// Copyright (C) 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.account;
+
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+
+import com.google.common.base.Throwables;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ImmutableSetMultimap;
+import com.google.common.collect.Streams;
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.server.account.externalids.ExternalId;
+import com.google.gerrit.server.account.externalids.ExternalIds;
+import com.google.gerrit.server.query.account.InternalAccountQuery;
+import com.google.gerrit.server.update.RetryHelper;
+import com.google.gerrit.server.update.RetryHelper.Action;
+import com.google.gerrit.server.update.RetryHelper.ActionType;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import java.io.IOException;
+
+/** Class to access accounts by email. */
+@Singleton
+public class Emails {
+  private final ExternalIds externalIds;
+  private final Provider<InternalAccountQuery> queryProvider;
+  private final RetryHelper retryHelper;
+
+  @Inject
+  public Emails(
+      ExternalIds externalIds,
+      Provider<InternalAccountQuery> queryProvider,
+      RetryHelper retryHelper) {
+    this.externalIds = externalIds;
+    this.queryProvider = queryProvider;
+    this.retryHelper = retryHelper;
+  }
+
+  /**
+   * Returns the accounts with the given email.
+   *
+   * <p>Each email should belong to a single account only. This means if more than one account is
+   * returned there is an inconsistency in the external IDs.
+   *
+   * <p>The accounts are retrieved via the external ID cache. Each access to the external ID cache
+   * requires reading the SHA1 of the refs/meta/external-ids branch. If accounts for multiple emails
+   * are needed it is more efficient to use {@link #getAccountsFor(String...)} as this method reads
+   * the SHA1 of the refs/meta/external-ids branch only once (and not once per email).
+   *
+   * <p>In addition accounts are included that have the given email as preferred email even if they
+   * have no external ID for the preferred email. Having accounts with a preferred email that does
+   * not exist as external ID is an inconsistency, but existing functionality relies on still
+   * getting those accounts, which is why they are included. Accounts by preferred email are fetched
+   * from the account index.
+   *
+   * @see #getAccountsFor(String...)
+   */
+  public ImmutableSet<Account.Id> getAccountFor(String email) throws IOException, OrmException {
+    return Streams.concat(
+            externalIds.byEmail(email).stream().map(ExternalId::accountId),
+            executeIndexQuery(() -> queryProvider.get().byPreferredEmail(email).stream())
+                .map(a -> a.getAccount().getId()))
+        .collect(toImmutableSet());
+  }
+
+  /**
+   * Returns the accounts for the given emails.
+   *
+   * @see #getAccountFor(String)
+   */
+  public ImmutableSetMultimap<String, Account.Id> getAccountsFor(String... emails)
+      throws IOException, OrmException {
+    ImmutableSetMultimap.Builder<String, Account.Id> builder = ImmutableSetMultimap.builder();
+    externalIds.byEmails(emails).entries().stream()
+        .forEach(e -> builder.put(e.getKey(), e.getValue().accountId()));
+    executeIndexQuery(() -> queryProvider.get().byPreferredEmail(emails).entries().stream())
+        .forEach(e -> builder.put(e.getKey(), e.getValue().getAccount().getId()));
+    return builder.build();
+  }
+
+  /**
+   * Returns the accounts with the given email.
+   *
+   * <p>This method behaves just like {@link #getAccountFor(String)}, except that accounts are not
+   * looked up by their preferred email. Thus, this method does not rely on the accounts index.
+   */
+  public ImmutableSet<Account.Id> getAccountForExternal(String email) throws IOException {
+    return externalIds.byEmail(email).stream().map(ExternalId::accountId).collect(toImmutableSet());
+  }
+
+  private <T> T executeIndexQuery(Action<T> action) throws OrmException {
+    try {
+      return retryHelper.execute(ActionType.INDEX_QUERY, action, OrmException.class::isInstance);
+    } catch (Exception e) {
+      Throwables.throwIfUnchecked(e);
+      Throwables.throwIfInstanceOf(e, OrmException.class);
+      throw new OrmException(e);
+    }
+  }
+}