[Python] How to send email from DigitalOcean droplet in python3 using local mail server to a...

I am trying to send email from a DigitalOcean droplet (Ubuntu 16.04 32 bit) in python3.5 using the local mail/smtp server, primarily to a gmail account. However, currently no errors are displaying from my python script or the server command, but the emails are not showing up in my gmail inbox or spam folder.

I have also followed similar steps from my laptop where possible, with no results.

I want to use the local mail/smtp server to send emails to avoid storing authentication details in the server, and since it will not be receiving emails then I am not as worried about security as if receiving (e.g. not worried about injection attack).

To start off, I run the command;

python3 -m smtpd -n -c PureProxy localhost:1025 &


I run the following script. My understanding is that this should send the email to the local mail/smtp server, which should then handle ensuring it's delivery.

import smtplib
from email.mime.text import MIMEText

msg = MIMEText('test message from droplet body')
msg['Subject'] = 'test message from droplet subject'
msg['From'] = 'droplet@mydomain.com.au'
msg['To'] = 'mygmailusername@gmail.com'

s = smtplib.SMTP('localhost', 1025)
s.set_debuglevel(True)
s.send_message(msg)
s.quit()


With the above method, no error messages occur. However the emails are never received. All methods I have tried so far have had this result.

Using the DebuggingServer instead of PureProxy and the same steps as before provides output similar to below;

---------- MESSAGE FOLLOWS ----------
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: test message from droplet subject
From: droplet@mydomain.com.au
To: mygmailusername@gmail.com
X-Peer: 127.0.0.1

test message from droplet body
------------ END MESSAGE ------------


I have tried the first example on the following page

https://docs.python.org/3/library/email-examples.html

However this fails due to a refused connection error.

I have also tried to check the spamminess of my domain's emails using the following site, however it times out - this indicates to me that it may be a problem with DigitalOcean allowing emails through it's firewall.

https://www.mail-tester.com/

I have checked reputation of my domain using this site - it says it is neutral (using talosintelligence link in comments)

I have tried sending email using the prior instructions to my namecheap private email, but without success.

One possibility I read about is that a PTR DNS record needs to be set, to allow reverse DNS lookup. I am not sure what to do with this though, and I would have to override the default droplet name.

Extra details

I am using a .com.au domain registered with namecheap. I am also using a private email service with namecheap, which required setting multiple DNS records including MX - I added all on the following link, including the optional ones, on my digitalocean account (link in comments)

I also set up the digitalocean nameservers on the namecheap account (link in comments)

I can send and receive email on the private email service.

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