I ran this by bibliophage before I posted, given the nature of the question.
I run a website (www.edentrap.com) for my band. It has voluntary registration so that I can “spam” users to let them know about upcoming gigs, announcements, things like that. The problem is that about half of the users are not getting the emails. I believe that their ISP’s overly protective spam filters are blocking me, and even Hotmail puts it in the junk folder.
Are there any steps I can take to avoid this? If it matters, it’s a Dot Net Nuke site and I’m using the Bulk Email utility. When sending the email I use the option to send individual personalized messages as opposed to a bulk “bcc:” and I thought that would be enough.
Thoughts or suggestions?
Why not get them to sign up for a mailing list? That way you post your message to the list for all recipents to read.
As for ISPs blocking your emails, you are pretty much SOL. You may very well be legitimate to them but creating exceptions to their spam rules is in the too hard basket.
There is a good possibility that your server is sending mail using the Windows equivalent of sendmail, with your domain name as the source, and sending via MX records directly to the mail server for the ISP of the recipients. AOL and other large ISPs check to see if the IP address resolves back to the domain name of the server they get the mail from. Your IP address does not resolve back to your domain because you have a virtual server.
All of this means that you need to have the send mail program that your virtual server uses route your outgoing mail through the smtp server that your ISP provides. IF you were on a UNIX type system using sendmail (which you ARE NOT) you would need to have a smtp: line in the mailertable file. Mine looks like this:
smtp:smtp.kamp-dsl.de
When you do this, AOL gets handed the email by your ISP’s mail server. That address will resolve back to the domain that it gives to AOL, and everything is fine.
I had this problem for a while myself. I run my own web and mail servers on DSL, and for a while I couldn’t send mail to anyone with an AOL address. With the entry I listed above, my mail get through to AOL just fine.
You might want to check your domain name or IP address at http://www.ordb.org to see if you’re blacklisted. Also the sites listed here. If your host’s IP has been blacklisted (not your fault), then you need to tell them what lists they are on and ask them to please take steps to remove their IPs.
Also, if you’re using any HTML in your emails, you might want to try to avoid that. Alot of anti-spam stuff is being set up to reject emails with HTML in them - even if you’re just trying to send your friend some HTML advice grumble…
Just be thankful you didn’t name your band “Teen Sluts.” 
What Duckster said. This is what LISTSERV and/or MAJORDOMO are for.
Alternatively, post your stuff on a web page and have people go to it with their browsers.
There are tips that would help you do what you’re asking about, but I won’t ever tell anyone any of what I know that might help them just in case someone who wishes to spam gets a chance to read it. Anything I tell you that would enable you to get past spam filters would help spammers get past spam filters.
Some spam filters like SpamAssassin (if configured to do so) add a detailed analysis to the headers. It lists which rules were triggered and how much they contributed to the classification.
If you can find a mail server using it, this information might help you.