Airflow的DAG中可以添加一个电子邮件任务，用于在任务失败时发送通知电子邮件。下面是示例代码：

from airflow import DAG
from airflow.operators.python_operator import PythonOperator, EmailOperator
from datetime import datetime, timedelta

default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': datetime(2021, 8, 1),
    'email_on_failure': True,
    'email': ['airflow@example.com'],
    'retries': 1,
    'retry_delay': timedelta(minutes=5),
}

dag = DAG(
    'example_dag',
    default_args=default_args,
    schedule_interval=timedelta(days=1),
)

def task1():
    # do something

def task2():
    # do something that may fail

def task3():
    # do something

task_1 = PythonOperator(
    task_id='task_1',
    python_callable=task1,
    dag=dag,
)

task_2 = PythonOperator(
    task_id='task_2',
    python_callable=task2,
    dag=dag,
    email_on_failure=True, # 设置任务失败后发送邮件通知
)

task_3 = PythonOperator(
    task_id='task_3',
    python_callable=task3,
    dag=dag,
)

email_task = EmailOperator(
    task_id='email_task',
    to=['admin@example.com'],
    subject='Airflow Task Failed',
    html_content="""
Airflow Task failed. Please check your DAG.
""",
    dag=dag,
)

task_1 >> task_2 >> task_3 >> email_task

在这个DAG中，当任务2失败时，Airflow会自动发送电子邮件通知到指定的收件人地址。