When sending, the received message in GMAIL (when opened) goes to the trash, how can I get around this?

Question

Django

I decided to make a newsletter for the site on DJANGO, connected the DJANGO-NEWSLETTER package. Everything seems to be working. But there is one problem.
The letter gets into Google mail - but when you try to open it, it automatically ends up in the trash.
You can go to the basket, and return to the inbox. But when you open it, it goes back to the trash.
And only if you send it to yourself, it goes into the basket only at the first opening, but not at the second.
What is it?
I send newsletters via SendGrid (Heroku) with the command
python manage.py submit_newsletter -v 2
(heroku-CLI)

Answer 1

Full breakdown here. My case is using Unroll.me
Disabled POP and IMAP in settings
The effect is gone.
Parsing

Answer 2

I think that the mailing program has nothing to do with it. Googled "mails forwarded to trash gmail" - the problem occurs.
From what is written there are two options:
To be honest, I don't see any other options.
Try sending email to other accounts and look at the behavior.

Answer 3

Perhaps forwarding is configured in the mail (like this https://www.unisender.com/ru/blog/haki/kak-nastroi... with automatic deletion of letters.