Ok, can someone explain to me why an address for "support" is hard coded into wmpu?
fgrep -r support@ *
wp-admin/wpmu-options.php: <?php printf( __( 'Registration and support mails will come from this address. Make it generic like "support@%s"' ), $current_site->domain ); ?>
wp-includes/class-phpmailer.php: var $From = "support@wordpress.com";
wp-includes/wpmu-functions.php: $admin_email = 'support@' . $_SERVER['SERVER_NAME'];
wp-includes/wpmu-functions.php: $admin_email = 'support@' . $_SERVER['SERVER_NAME'];
wp-includes/wpmu-functions.php: $admin_email = 'support@' . $_SERVER['SERVER_NAME'];
wp-includes/wpmu-functions.php: $admin_email = 'support@' . $_SERVER['SERVER_NAME'];
wp-settings.php: graceful_fail(sprintf(__('This blog has not been activated yet. If you are having problems activating your blog, please contact support@{%1$s}.'), $current_site->domain));
Furthermore, checking my mail logs, I find that emails are trying to be sent as support@blogname.sitename.com, e.g.
Jan 6 11:06:10 descartes sendmail[3724]: m06G69vb003724: to=kkmein12@21cn.com, ctladdr=support@kkmein12.bitfreedom.com (1000/1000), delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=30752, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (m06G69HZ003725 Message accepted for delivery)
This is not good. All email should be sent as whatever I have set as "Site Admin Email" instead. Subdomains of a wpmu installation aren't even necessarily real domains with MX records!