airflow EmailOperator throws "smtplib.SMTPNotSupportedError: STARTTLS extension not supported by server"?

Question

Trying to use airflow's EmailOperator to send an email on trigger_rule.ONE_FAILED and seeing error:

[2019-10-14 13:31:50,604] {configuration.py:206} WARNING - section/key [smtp/smtp_user] not found in config
Traceback (most recent call last):
   File "/bin/airflow", line 27, in <module>
[     args.func(args)
   File "/usr/lib/python2.7/site-packages/airflow/bin/cli.py", line 392, in run
     pool=args.pool,
   File "/usr/lib/python2.7/site-packages/airflow/utils/db.py", line 50, in wrapper
     result = func(*args, **kwargs)
   File "/usr/lib/python2.7/site-packages/airflow/models.py", line 1493, in _run_raw_task
     result = task_copy.execute(context=context)
   File "/usr/lib/python2.7/site-packages/airflow/operators/email_operator.py", line 64, in execute
     send_email(self.to, self.subject, self.html_content, files=self.files, cc=self.cc, bcc=self.bcc, mime_subtype=self.mime_subtype)
   File "/usr/lib/python2.7/site-packages/airflow/utils/email.py", line 44, in send_email
     return backend(to, subject, html_content, files=files, dryrun=dryrun, cc=cc, bcc=bcc, mime_subtype=mime_subtype)
   File "/usr/lib/python2.7/site-packages/airflow/utils/email.py", line 87, in send_email_smtp
     send_MIME_email(SMTP_MAIL_FROM, recipients, msg, dryrun)
   File "/usr/lib/python2.7/site-packages/airflow/utils/email.py", line 109, in send_MIME_email
     s.starttls()
   File "/usr/lib64/python2.7/smtplib.py", line 643, in starttls
     raise SMTPException("STARTTLS extension not supported by server.")
 smtplib.SMTPException: STARTTLS 

Have not changed the default airflow.cfg (other than for basic password authentication to access the webserver) and the email portion looks like

[email]
email_backend = airflow.utils.email.send_email_smtp


[smtp]
# If you want airflow to send emails on retries, failure, and you want to use
# the airflow.utils.email.send_email_smtp function, you have to configure an
# smtp server here
smtp_host = localhost
smtp_starttls = True
smtp_ssl = False
# Uncomment and set the user/pass settings if you want to use SMTP AUTH
# smtp_user = airflow
# smtp_password = airflow
smtp_port = 25
smtp_mail_from = airflow@example.com

Checking the port in the cfg file, it seems to be open and listening...

[rvillanueva@mapr001 queensetl_airflow]$ netstat -plnt | grep ':25'
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      -                   
tcp6       0      0 ::1:25                  :::*                    LISTEN      -  

... and I am able to use the linux sendmail bash command for other process that run on this same machine (CentOS 7).

Anyone know what could be going on here or any further debugging tips?

Answer 1

After help from the airflow users mailing list and from the error trace shown above, the thing that fixed this problem was just setting smtp_starttls = False.

Testing with a script like...

# Import smtplib for the actual sending function
import smtplib
from email.mime.text import MIMEText

send_to = 'myaddress@co.org'
msg = MIMEText('Hello World')
msg['Subject'] = 'Test Airflow Email'
msg['From'] = 'airflow@example.com'
msg['To'] = send_to

# SMTP Send
s = smtplib.SMTP('localhost')
s.starttls() # Try commenting out this line and see if you get a different error
s.sendmail(me, [send_to], msg.as_string())
s.quit()

saw the same error and was able to get rid of it by commenting out the s.starttls() line. So now my airflow.cfg file looks like...

[smtp]
# If you want airflow to send emails on retries, failure, and you want to use
# the airflow.utils.email.send_email_smtp function, you have to configure an
# smtp server here
smtp_host = localhost
#smtp_starttls = True
smtp_starttls = False
smtp_ssl = False
# Uncomment and set the user/pass settings if you want to use SMTP AUTH
# smtp_user = airflow
# smtp_password = airflow
smtp_port = 25
smtp_mail_from = airflow@example.com

and email alerts appear to be working fine.