Except you can block read receipts in most sane mail clients (Thunderbird has options for always/prompt/never for example). It doesn't appear that there is a wa

Except you can block read receipts in most sane mail clients (Thunderbird has options for always/prompt/never for example). It doesn't appear that there is a way to block your messages being marked as 'seen' on Facebook, unless it's buried deep in the frequently-changing privacy settings.