hello, I need help to correctly configure the sending and receiving of mail.

I have a properly configured administrator account, the mails are sent and received.

but I also created two other account (seller and buyer) with their own email address, which they can not send mail (sales module> quote and purchase module> price request)

I configure the incoming and outgoing servers for the three accounts (admin, seller and buyer).
(When I test, the one of the admin works, not the others ...
and yet the config is good and works very well with thunderbird for example)

I check "access to private address" in their configuration.

Failed to send email via SMTP server 'None'.
SMTPRecipientsRefused: {'customer@mygoodadresse.com': (553, b'5.7.1 <seller@mygoodadresse.com>: Sender address rejected: not owned by user admin ')

when I try to send an email from the admin account
(technical > emails  >creates)
with the seller's email, I have this error:

The requested operation can not be performed because of the security policy. Please contact your system administrator.
(Document type: Message, Operation: read)

where and how to configure that ?
thank you in advance.

(escuse my google translation from french)