Will a 'mailto' link in an Auto-Response email break Case Threading and if yes, which are possible standard solutions?

Hi everyone,

 I need some architectural advice regarding Email Threading for following scenario:

• When a Case is created, a Lightning Email Template is sent via Flow.
• The business wants a 'mailto' hyperlink in the email body so the customer can click it to send a follow-up email.
• This mailto link is configured to pre-fill the recipient (support@company.com) and the Subject line with the Case Number (e.g., Re: Case 00123456).

The Problem:  My assumption is that if a customer uses this mailto link, it creates a brand new email in their client (Outlook/Gmail). Since this new email lacks the original Message-ID headers (In-Reply-To / References) and the Thread ID (if using the old string-based threading), Salesforce will not be able to associate this incoming email with the existing Case, resulting in a duplicate Case.

My Questions:

1. Is my assumption correct that a standard mailto link breaks the threading logic in Salesforce Service Cloud?
2. Is there any declarative way (Flow/Standard Config) to ensure these replies attach to the original Case based solely on the Subject line containing the Case Number?
3. Or does this require Custom Development (e.g., an Apex Inbound Email Handler) to manually parse the Subject and link the email to the correct Case?

The sent of such emails should be considered for the channels email-to-case, manual and portal.

Thanks in advance for your help!    @Salesforce Administrators & Developers @Salesforce Administrators and Developers  @* Outlook/Teams, Gmail, and Inbox * @* Service Cloud *