diff --git a/docs/usage_overview.rst b/docs/usage_overview.rst
index d7cfb8250..a321afb93 100644
--- a/docs/usage_overview.rst
+++ b/docs/usage_overview.rst
@@ -161,6 +161,9 @@ These are as follows:
     will not consume flagged mails.
 *   **Move to folder:** Moves consumed mails out of the way so that paperless wont
     consume them again.
+*   **Add custom Tag:** Adds a custom tag to mails with consumed documents (the IMAP
+    standard calls these "keywords"). Paperless will not consume mails already tagged.
+    Not all mail servers support this feature!
 
 .. caution::
 
diff --git a/src/paperless_mail/mail.py b/src/paperless_mail/mail.py
index 67cc22130..fefcbda5e 100644
--- a/src/paperless_mail/mail.py
+++ b/src/paperless_mail/mail.py
@@ -62,6 +62,17 @@ class FlagMailAction(BaseMailAction):
         M.flag(message_uids, [MailMessageFlags.FLAGGED], True)
 
 
+class TagMailAction(BaseMailAction):
+    def __init__(self, parameter):
+        self.keyword = parameter
+
+    def get_criteria(self):
+        return {"no_keyword": self.keyword}
+
+    def post_consume(self, M: MailBox, message_uids, parameter):
+        M.flag(message_uids, [self.keyword], True)
+
+
 def get_rule_action(rule):
     if rule.action == MailRule.MailAction.FLAG:
         return FlagMailAction()
@@ -71,6 +82,8 @@ def get_rule_action(rule):
         return MoveMailAction()
     elif rule.action == MailRule.MailAction.MARK_READ:
         return MarkReadMailAction()
+    elif rule.action == MailRule.MailAction.TAG:
+        return TagMailAction(rule.action_parameter)
     else:
         raise NotImplementedError("Unknown action.")  # pragma: nocover
 
diff --git a/src/paperless_mail/migrations/0015_alter_mailrule_action.py b/src/paperless_mail/migrations/0015_alter_mailrule_action.py
new file mode 100644
index 000000000..62a44e6aa
--- /dev/null
+++ b/src/paperless_mail/migrations/0015_alter_mailrule_action.py
@@ -0,0 +1,28 @@
+# Generated by Django 4.0.4 on 2022-05-29 13:21
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("paperless_mail", "0014_alter_mailrule_action"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="mailrule",
+            name="action",
+            field=models.PositiveIntegerField(
+                choices=[
+                    (1, "Delete"),
+                    (2, "Move to specified folder"),
+                    (3, "Mark as read, don't process read mails"),
+                    (4, "Flag the mail, don't process flagged mails"),
+                    (5, "Tag the mail with specified tag, don't process tagged mails"),
+                ],
+                default=3,
+                verbose_name="action",
+            ),
+        ),
+    ]
diff --git a/src/paperless_mail/models.py b/src/paperless_mail/models.py
index 4e90197b7..4c0a1a557 100644
--- a/src/paperless_mail/models.py
+++ b/src/paperless_mail/models.py
@@ -65,6 +65,7 @@ class MailRule(models.Model):
         MOVE = 2, _("Move to specified folder")
         MARK_READ = 3, _("Mark as read, don't process read mails")
         FLAG = 4, _("Flag the mail, don't process flagged mails")
+        TAG = 5, _("Tag the mail with specified tag, don't process tagged mails")
 
     class TitleSource(models.IntegerChoices):
         FROM_SUBJECT = 1, _("Use subject as title")
diff --git a/src/paperless_mail/tests/test_mail.py b/src/paperless_mail/tests/test_mail.py
index 24014b4dc..2aaa588d6 100644
--- a/src/paperless_mail/tests/test_mail.py
+++ b/src/paperless_mail/tests/test_mail.py
@@ -96,6 +96,10 @@ class BogusMailBox(ContextManager):
         if "UNFLAGGED" in criteria:
             msg = filter(lambda m: not m.flagged, msg)
 
+        if "UNKEYWORD" in criteria:
+            tag = criteria[criteria.index("UNKEYWORD") + 1].strip("'")
+            msg = filter(lambda m: "processed" not in m.flags, msg)
+
         return list(msg)
 
     def delete(self, uid_list):
@@ -109,6 +113,9 @@ class BogusMailBox(ContextManager):
                         message.flagged = value
                     if flag == MailMessageFlags.SEEN:
                         message.seen = value
+                    if flag == "processed":
+                        message._raw_flag_data.append(f"+FLAGS (processed)".encode())
+                        MailMessage.flags.fget.cache_clear()
 
     def move(self, uid_list, folder):
         if folder == "spam":
@@ -130,6 +137,7 @@ def create_message(
     from_: str = "noone@mail.com",
     seen: bool = False,
     flagged: bool = False,
+    processed: bool = False,
 ) -> MailMessage:
     email_msg = email.message.EmailMessage()
     # TODO: This does NOT set the UID
@@ -175,6 +183,9 @@ def create_message(
 
     imap_msg.seen = seen
     imap_msg.flagged = flagged
+    if processed:
+        imap_msg._raw_flag_data.append(f"+FLAGS (processed)".encode())
+        MailMessage.flags.fget.cache_clear()
 
     return imap_msg
 
@@ -217,6 +228,7 @@ class TestMail(DirectoriesMixin, TestCase):
                 body="cables",
                 seen=True,
                 flagged=False,
+                processed=False,
             ),
         )
         self.bogus_mailbox.messages.append(
@@ -225,6 +237,7 @@ class TestMail(DirectoriesMixin, TestCase):
                 body="from my favorite electronic store",
                 seen=False,
                 flagged=True,
+                processed=True,
             ),
         )
         self.bogus_mailbox.messages.append(
@@ -571,6 +584,29 @@ class TestMail(DirectoriesMixin, TestCase):
         self.assertEqual(len(self.bogus_mailbox.messages), 2)
         self.assertEqual(len(self.bogus_mailbox.messages_spam), 1)
 
+    def test_handle_mail_account_tag(self):
+        account = MailAccount.objects.create(
+            name="test",
+            imap_server="",
+            username="admin",
+            password="secret",
+        )
+
+        _ = MailRule.objects.create(
+            name="testrule",
+            account=account,
+            action=MailRule.MailAction.TAG,
+            action_parameter="processed",
+        )
+
+        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+        self.assertEqual(self.async_task.call_count, 0)
+        self.assertEqual(len(self.bogus_mailbox.fetch("UNKEYWORD processed", False)), 2)
+        self.mail_account_handler.handle_mail_account(account)
+        self.assertEqual(self.async_task.call_count, 2)
+        self.assertEqual(len(self.bogus_mailbox.fetch("UNKEYWORD processed", False)), 0)
+        self.assertEqual(len(self.bogus_mailbox.messages), 3)
+
     def test_error_login(self):
         account = MailAccount.objects.create(
             name="test",