The Received header is not defined by eM Client, but the SMTP server that processes the message.

We send the EHLO command to the SMTP server as defined in RFC 5321.
Your mail server adds the full address-literal into the Recieved header, which is recommended by the specification.

User-Agent is also standard information given to the server, to identify the source of the email, though other apps can use different non-standard headers for the same reasons, such as X-Mailer (X-Mailer: iPad Mail (18C66) , X-Mailer: Microsoft Outlook 16.0,...).

So these details cannot be removed from your outgoing messages.