Hi,

1. Email

    Sends a real email to the recipient’s mailbox (via outgoing mail server).

    The mail goes out through ir.mail_server → reaches the client’s inbox.

    You’ll see it in the Chatter under the Messages tab with a ✉️ icon.

    Client can reply to it, and depending on your catchall/reply-to setup, it can come back into Odoo.

2. Message

    Sends an internal message in the record’s chatter.

    Stays inside Odoo (like an internal note but visible in the Messages section).

    No external email is sent.

    Useful for logging, team communication, or automation that should stay internal only.

Since you said “send emails to clients”, you should select Email.

If you pick Message, your clients won’t receive anything outside Odoo.

Hope it helps