When using "mail-to" list unscubscribe clearly indicate that the process will mark the message as "failed"

Issue in ./help/additional-resources/acc-technical-recommendations.md

In this section of documentation, https://experienceleague.adobe.com/en/docs/deliverability-learn/deliverability-best-practice-guide/additional-resources/campaign/acc-technical-recommendations#mailto-list-unsubscribe, we need to add in a statement that doing the List Unsubscribe will mark the email as "Failed"

This was oultined from a Customer Care ticket, E-002144518

> the behavior you described aligns with the existing product design for email_client_unsubscribe. When a recipient uses the unsubscribe option directly from an email client such as Gmail, Campaign processes this as a global opt-out, updates the recipient to “No longer contacted by any channel,” and marks the associated delivery logs as failed accordingly.

Having this clearly identified in the documentation will help to avoid future customer care complaints or issues.

Thanks,
Michael

Open ./help/additional-resources/acc-technical-recommendations.md and read the mail-to list unsubscribe section at the linked anchor. Update the documentation to state that using List-Unsubscribe marks the associated email as "Failed," then verify the rendered section clearly reflects the documented behavior.

Written by the indexing model from the issue text.