Scheduled emails failing - HELP
Lots of digging here:
The culprit is Bluehost shared hosting AND VERP (variable envelope return processing), which is an interesting hack and very useful for massive systems.  (I am a colleague of Ray Tomlinson and something of a dinosaur when it comes to email protocols ...)

Bluehost is my shared hosting provider (no VERP) and VERP is - well, a hack.  VERP SHOULD be handled with extra header settings but is done as a sender NAME which violates all kinds of identity-based authentication protections - but then I'm a security expert and so I do have opinions.

Technical answer:
Bluehost (and most others) do not support VERP unless you pay for a VPS or better plan.

CiviCRM - being intended for big players - requires VERP to handle bounces and other issues when dealing with large mailing lists.   (Kudos to CiviCRM)

My 501(c)3 is neither a big player (fewer than 20 recipients) nor willing to pay for a VPS (because we're small ...) and not willing to pay for a for-profit CRM (because we're small).

The answer for people in a similar situation to me is to edit out a portion of smtp.php (in the civicrm folder) and comment out:

/*if (!empty($headers['Return-Path'])) {
        $from = $headers['Return-Path'];
    }*/    


smtp.php = (cd civicrm folder; exec find . -name smtp.php -a -print;)

The CiviCRM people (bless them for their efforts !) will rightfully claim that my, and other's, 'solution' is a hack (VERP is a hack too, but useful ...) that should be deprecated with excessive force, but they should also allow the ability for us small folks who have *NO OTHER FREE AND OPEN SOURCE SOLUTIONS* an option as part of the configuration.  

Love an kisses ...