Multiple recipient email delivery best practices?

In my app, I've got products that a user can subscribe to emails
updates...when somebody updates the product's attributes, they get an
email.

My question is how do I deliver that email so that all the user's
email addresses are NOT in the "TO:" line, only the individual's email
address? I'm currently sending my mailer an array of email
addresses. Is that bad form? Should I instead loop over each user
subscribed to email alerts and call my mailer once for each user?
That seems like bad practice...

Thanks for any advice.

This is what Bcc: is for.. populating the envelope without the users
knowing about each other.

Ok so the 'recipients' field is not required then...I can simply swap
'recipient' for 'bcc'? That sounds easy enough...thanks.

Ok so the 'recipients' field is not required then...I can simply swap
'recipient' for 'bcc'?

That's right

That sounds easy enough...thanks.

The advantage for your users is that their e-mail addresses are not disclosed.

The advantage for you is that it is only one e-mail, with a single message ID, out to your SMTP smarthost & perhaps beyond.

http://en.wikipedia.org/wiki/Blind_carbon_copy

Regards

Thanks the help!