A newsletter is a marketing channel that consists of a letter sends as an email to many users.
See Email
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
See Open
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"