How to use Mailgun's recipient-variables with Django SMTP mail backend?

Question

How can I properly send batch/bulk/mass emails using MailGun in Django using SMTP protocol?

What I've tried so far?

• I am using django.core.mail.backends.smtp.EmailBackend as my EMAIL_BACKEND

and this is the code snippet that I have tried to send the emails.

from django.core.mail import EmailMultiAlternatives
import json

to_emails = [
    "mail_1@example.com",
    "mail_2@example.com",
    "mail_3@example.com",
    "mail_4@example.com",
    "jerinpetergeorge@gmail.com",
]
mail = EmailMultiAlternatives(
    subject="Hey - %recipient.name%",
    body="Hey %recipient.name%,\n\nThis is just a batch email test!!!",
    from_email="JPG <me@somehost.com>",
    to=to_emails,
)
recipient_variables = {
    address: {"name": address} for address in to_emails
}
mail.extra_headers["X-Mailgun-Recipient-Variables"] = json.dumps(recipient_variables)
response = mail.send()
print(response)

and I've got the mail as below,

As we can see, the to attribute is filled with all email addresses, which is not what I am expecting.

So, how can I tell the Mailgun/Django to parse my variables properly in order to make the emails looks more personal?

---

Notes

• I prefer to use SMTP protocol
• I've tried the REST APIs of Mailgun and it was a success (but, I prefer SMTP)
• I found django-anymail and seems it has the feature. But, It also uses the APIs (correct me if I am wrong)

---

Update-1

• Updated the to argument to to="%recipient%" But, got

  • TypeError: "to" argument must be a list or tuple

• Updated the to argument to to=["%recipient%"] But, got

  • smtplib.SMTPRecipientsRefused: {'=?utf-8?q?=25recipient=25?=': (501, b'Invalid command or cannot parse to address')}

Answer 1

As we can see, the to attribute is filled with all email addresses, which is not what I am expecting.

It is not properly supported with SMTP by Mailgun.

However, relying on the (unintuitive) implementation of BCC in Mailgun, there is a workaround:

mail = EmailMultiAlternatives(
    subject="Hey - %recipient.name%",
    body="Hey %recipient.name%,\n\nThis is just a batch email test!!!",
    from_email="JPG <me@somehost.com>",
    # to=to_emails,  # Replace this
    bcc=to_emails,   # with this
)
recipient_variables = {
    address: {"name": address} for address in to_emails
}
mail.extra_headers["To"] = "%recipient%"  # Add this
mail.extra_headers["X-Mailgun-Recipient-Variables"] = json.dumps(recipient_variables)

Reference: https://stackoverflow.com/questions/37948729/mailgun-smtp-batch-sending-with-recipient-variables-shows-all-recipients-in-to-field

---

1. Why does to=["%recipient%"] not work with SMTP?

It's the standard in the protocol.

From https://documentation.mailgun.com/_/downloads/en/latest/pdf/:

SMTP send will error with “cannot parse to address” or “cannot parse from address” if the provided email address fails syntax checks in accordance with RFC5321, RFC5322, RFC6854.

2. What to do for proper support of Batch Sending with Mailgun?

Use the API.

From https://stackoverflow.com/questions/30787399/laravel-5-sending-group-emails (multiposted to https://laracasts.com/discuss/channels/laravel/sending-email-to-1000s-of-reciepents):

So far, I have created an array of recipient email addresses, sent the email to a webmaster type address, and included the end recipients in BCC

While this works, it's not ideal.

Rather than using Laravel's built in Mail, I elected to use Mailgun's API (specifically batch sending) directly

This also allows me to access unique recipient variables within my email template

(It's not specific to Laravel/PHP, but to SMTP via Mailgun.)

3. What do you mean by "unintuitive" implementation of BCC in Mailgun?

Mailgun effectively personalises the email for each BCC recipient using recipient-variables.

From https://github.com/mailgun/mailgun-js-boland/issues/89:

the bcc person is receiving the email as it was addressed to them instead of being part of the bcc

This causes a separate issue when you actually want BCC recipients to get the same content.

From https://stackoverflow.com/questions/48887866/bcc-in-mailgun-batch-send-does-not-include-substitutions:

In the copy sent to the bcc address, the recip_vars substitution has not been made.

According to the good people at Mailgun, this is not possible, at least in the current release of the service.