I'm going to be emailing all of my site users to update them on recent developments and remind them to come back to the site.  Are there any special precautions I should take.  I was going to do this through a loop in PHP.  I have about 1,000 users.
Emailing all site users
php;email;spam
Generally you'll want to avoid being detected as SPAM through using the right content and DNS records.Sending 10 or more similar emails to a domain in a 30 minute window has also caused us some issues in the past (do not know the cause and it only affects a few domains). So we tend to make batches (in a scripting language such as PHP) then send through a script either using cron or at.Limit the number of emails sent in each batch and monitor for rejections and abuse@/spam@ replies. Using receipts and unique tracking images will also help you determine the number of emails received. Unfortunately there is no one-size-fits-all solution when it comes to the sending side, but by being proactive you'll find the gaps that need plugged.