okay, i have achieved complete success in sending mail via PHP mail() , although the successful settings are not what i prefer, and i think my findings are remarkable, so i'd like to post them for comment, or maybe it will help someone else somehow.
only one of my domains are hosted on a different server. i'll call it myFirstServer.com. he uses BSDI (unix) and apache. i know that some things are different there, like where i can execute Perl scripts for example, and how to address the smtp (i've had to use different settings in my Perl mail scripts for myFirstServer.com than i do for mySecondServer.com).
in both http.conf and php.ini i have the entered the same e-mail address: ServerAdmin mymail@mySecondServer.com, and sendmail_from = mymail@mySecondServer.com, respectively.
i want to use mySecondServer.com for all of these settings because i eventually will likely move my domain from myFirstServer.com to mySecondServer.com.
if i set in php.ini SMTP = myFirstServer.com (and leave sendmail_from and ServerAdmin to mymail@mySecondServer.com), my PHP mail() script sends to every e-mail address in the MySQL db which that script accesses, including of course my free e-mail accounts. so, as far as i can tell, it works with that setting.
however, if i change that one setting in php.ini to SMTP = mySecondServer.com or mail.mySecondServer.com, my PHP mail() function only sends to mymail@mySecondServer.com and i get Warning errors for all other accounts (including mymail@myFirstServer.com), as i mentioned in my post directly above this one.
so, taking into consideration the behaviors ive cited here, do you have any idea why i get the errors for mySecondServer.com, why it DOES work w/ SMTP = myFirstServer.com, and what i might do to work around this "problem"?
for now, of course i can still use SMTP = myFirstServer.com , but preparing for impending change, i will ultimately need for SMTP = mySecondServer.com to work properly.
in the meantime, i'm going to contact Admin at mySecondServer.com to see what they have to say about this.