I assume this generates an error, right?

Yes, the mailserver doesn't like the mail and sends a note to the sender (in my case the owner of the process, user www-data).

You haven't configured Mantis to put the users in Bcc, I take it?

It sounds as if this is only a problem when no one is getting a mail (i.e. no recipients)? Is that correct?

yes, that seems to be correct. I haven't checked the other options, but the email seems to have no recipients at all..

And is that what is supposed to happen, or is it supposed to be sent to some recipients?

Mantis beaves correctly, no one should receive an email... but mantis shouldn't send an email if there are no recipients...

Quite.

As far as I can tell from the code, it shouldn't send any mail:

(from email_send:)

short-circuit if no recipient is defined
if ( is_blank( $p_recipient ) && ( OFF == config_get('use_bcc') ) ) {

return;

}

is_blank even returns true if there is only whitespace in $p_recipient. Can you confirm that $g_use_bcc is set to OFF? And if so, can you see what the value of $p_recipient is when the problem occurs?

Following are my comments:

• The use_bcc is an absolete configuration now, since we are sending an email per user. This should be removed from config_defaults_inc.php and added to core/obsolete.php.
• The use_bcc is defaulted to ON, hence, this may cause the check for empty receipients to fail, and hence still attempt to send the email.

As per the current code, the line Jeroen highlighted is the only place where this config is used in core/email_api.php.

fixed in CVS. removed to_mail and use_bcc config options.