Add header to jinja2 template

airflow/providers/smtp/notifications/smtp.py

@@ -33,7 +33,7 @@
 SMTP_DEFAULT_TEMPLATED_SUBJECT_PATH = conf.get(
     "smtp",
     "templated_email_subject_path",
-    fallback=(Path(__file__).parent / "templates" / "email_subject.jinja").as_posix(),
+    fallback=(Path(__file__).parent / "templates" / "email_subject.jinja2").as_posix(),
 )
 
 

airflow/providers/smtp/notifications/templates/email_subject.jinja2

@@ -0,0 +1,23 @@
+{#
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you 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.
+#}
+{% if ti is defined %}
+DAG {{ ti.dag_id }} - Task {{ ti.task_id }} - Run ID {{ ti.run_id }} in State {{ ti.state }}
+{% elif slas is defined %}
+SLA Missed for DAG {{ dag.dag_id }} - Task {{ slas[0].task_id }}
+{% endif %}