questions about mail() function

[irc]

When using the mail() function, what happens to the undelivered mail. Is there a header that I can add to send the errors to a particular email address? Should I be asking my ISP about this?

Also, I am setting up a way for me to send a monthly e-mail to my users. I am going to have this process semi-automated and it will pull info from the database. In any case, should I have the php script process the mailing in small batches, say 30 at a time? Or should I can I process 500-1000 calls to the mail() function in one batch? Is it a problem to send one message to 500 email addresses using one call to the mail() function?

[Conscience]

for an automated monthly job I would be looking at simply using a cron job. - that would probably be the easiest.

[irc]

Well, I don't know what a cron job is... Also, I want to do some fairly dynamic stuff where I pull stuff from mySQL into the mailing. I think I know how to do this in PHP/mySQL... that's why I'm asking.