Multiple emails

Hi all, I have a list of email addresses pulled from a database and I want to send out an email to all of them (they are the registered users of this particular site). For the first issue of the newsletter I expect to have about 4000 people, but that will probably go up significantly in future issues. I can do the sending email normally and extraction of addresses, but my question was really a more general one. Is there anything I should be doing different when sending to so many? Is it better to send a load of addresses altogether (in bcc for example) for each mail call? how many? or is it better to use a mail call for each address? I did a few quick speed test and mail seemed to be very fast. I guess this way would have the advantage of being able to personallise for each person. And is there a possibility that my mails would be blocked my some kind of spam filtering system? Its not I might add! Any advice and past experience would be very welcome. BTW, my system is apache on linux, php 4.0.4pl1 running on a cobalt raq. Thanks in advance Tom Carter Web Architect roundcorners ltd.