A newsletter is a marketing channel that consists of a letter sends as an email to many users.
See Newsletter (mailing list, subscription form)
New domains are cheap. You don't spam from mybiz.com. You spam from mybizmail.com, mybizmarketing.com, mybizoffers.com, etc.
For instance:
They don't all do it, but many do.
And if they burn their main domain, it's an easy option.
Example of newsletter Mail Information
from: Thomas <[email protected]>
reply-to: Thomas <[email protected]>
to: Nico <[email protected]>
date: 4 Oct 2019, 09:38
subject: Nico, ....
mailing list: 148662d91563921f62f4d682amc list <148662d91563921f62f4d682a.141977.list-id.mcsv.net> Filter messages from this mailing list
mailed-by: mail154.sea81.mcsv.net
Signed by: example.com
security: Standard encryption (TLS) Learn more
Ref - Gmail - Oneclick Unsubscribe
To set up one-click unsubscribe. Include one or both of this headers
List-Unsubscribe-Post: List-Unsubscribe=One-Click
List-Unsubscribe: <https://your-company-net/unsubscribe/example>
or with a mailto scheme
List-Unsubscribe: <mailto:[email protected]?subject=unsubscribe>
If both headers are included, Gmail uses the one listed first.
When a user unsubscribes using one-click, you receive this POST request:
POST /unsubscribe/example HTTP/1.1
Host: your-company.net
Content-Type: application/x-www-form-urlencoded
Content-Length: 26
List-Unsubscribe=One-Click"