GMails custom domain "send as" discontinues January 2027

From January 2027 Gmail will no longer support “Send as” for third-party addresses (e.g., @yahoo.com, @outlook.com); Google Workspace aliases and Gmail-owned addresses remain usable. Users may add up to 99 custom “Send mail as” addresses but must configure SMTP and verify each one, with invalid or removed aliases causing bounce messages. Replies to an alias default to the original Gmail address unless both the default “From” and “reply-to” fields are changed.