How to send mail from another email address?

Question

Email

There is a service with the site.ru domain.
The service has clients who have their own email addresses registered wherever possible (their own domains, mail services, etc.):
[email protected]
[email protected]
[email protected]
[email protected] site.org
I need to take their email and do a mailing list from it (something similar is done by the sendpulse.com service) When
you receive such a letter, the signature "via" appears in gmail

something else)?

Answer 1

sending mail via relay

Answer 2

In general, no way, because at least public mail services either already use a strict DMARC policy or are in the process of implementing it, and it will not be possible to send letters from their addresses without authorization.