The email client exposes the sender’s real IP address in the Received header when sending via SMTP, and there is no built-in option to route through a proxy or anonymizing relay to protect the sender’s privacy.

Dear Thunderbird Team, I am writing to report a privacy concern and request a feature that would allow users to hide their real IP address when sending emails through SMTP. When I send an email using Thunderbird with a standard SMTP account (e.g., QQ Mail, Gmail, Outlook), the receiving mail server adds a `Received` header that contains my real public IP address. For example: ```text Received: from ehlo.thunderbird.net ([2409:8a20:1843:3590:xxxx:xxxx:xxxx:cde2]) by newxmesmtplogicsvrszc50-0.qq.com (NewEsmtp) with SMTP id B2A37C97; Fri, 25 Sep 2026 12:44:42 +0800 ``` In this case, `[2409:8a20:1843:3590:xxxx:xxxx:xxxx:cde2]` is my real public IPv6 address. Any recipient who views the full email headers can see my IP address and infer my network location and ISP. This is a significant privacy leak, especially for users who need to protect their identity or location. Currently, Thunderbird does not provide an easy way to prevent this. Even if I change the `EHLO` argument, the receiving server still records the IP address of my connection. The only practical workaround is to manually set up a proxy or a mail relay outside the client, which is not user-friendly. I would like to request the following: 1. Built-in proxy support – Allow users to send SMTP traffic through a SOCKS or HTTP proxy, so the receiving server sees the proxy’s IP instead of the user’s real IP. 2. Relay/anonymization option – Provide a simple way to configure an external SMTP relay that strips or replaces the original `Received` headers before forwarding. 3. Documentation or guidance – If a full feature is not feasible, at least provide official documentation on how to hide the sender’s IP using existing tools (e.g., Tor, VPN, or a custom relay). 4. Privacy setting – Consider adding a privacy option that warns users when their real IP will be exposed in outgoing SMTP headers. Steps to reproduce: 1. Configure Thunderbird with a standard SMTP account (e.g., QQ Mail). 2. Send an email to any recipient. 3. Ask the recipient to view the full email headers. 4. Observe the `Received` header containing your real public IP address. Expected behavior: The client should offer a way to anonymize the sender’s IP address when sending via SMTP, either through a built-in proxy setting or by supporting an external relay that can strip identifying headers. Actual behavior: The client sends the email directly from the user’s device, and the receiving server records the real IP address in the `Received` header, which is then visible to all recipients. I understand that SMTP servers often log source IPs for anti-spam purposes, and that the client cannot control what the server adds. However, by providing proxy or relay support, the client can give users a choice to protect their privacy. Thank you for considering this request. I believe many privacy-conscious users would benefit from such a feature. Sincerely, wyxtld