Lynn, thanks! Great question. Here are some general suggestions, things I would do if I were in your shoes.
- Move this mail to an ESP (email service provider). Yeah, somebody with a lot of technical savvy could do it on their own with a perl script or send it from their ISP email account. But, not everybody has that level of savvy, and it's a waste of time, in my opinion, to try to figure this out on your own. ESPs are experts at stuff like this. I think you should consider utilizing an ESP geared toward little bitty senders like Constant Contact or MailChimp.
- Don't try to send this email off of a dedicated IP address. 350 email messages a month isn't enough mail to build a solid reputation under the mechanisms employed by the top consumer ISPs. You're just not going to get to a point where you have solid inbox delivery. That's why moving it to an ESP helps; in particular, an ESP geared toward smaller lists is going to group your mail together with other folks' mail, sending it from a “shared” IP address or shared pool of IP addresses. It'll deliver much more reliably as a result.
- Don't attach the PDF to the email message. Link to it, instead. Spam filters are suspicious of attachments. Including an attachment in your email makes your message more likely to be filtered or blocked by a spam filter. You'll find that most ESPs don't allow attachments, and that's why. If you need a free and easy place to store the PDF, check out Google Sites. I use it to host the PDF menu for my friend's hot dog stand, Wiener and Still Champion, and it works great.
- People may come and go in the group, but resist the urge to send with different from addresses for group chairs, for individuals. Stick with a specific from address for all mailings, one that references the group, not the individual. An unchanging from address drives more reliable delivery. It also allows individual recipients to whitelist that from address, and when they do that by adding it to their address book or safe list, it'll further improve delivery to those people. Changing the from address periodically breaks that cycle. Varying the from address from mailing to mailing also makes it more likely that a recipient will forget who you are and report your mail as spam.
- You mentioned people at Hotmail not receiving the email message. "Silent discarding" of mail at Hotmail is a somewhat common (and irritating) problem faced by senders, especially small senders or new senders. If you're going to tackle this on your own, two things need to happen: You need to implement an SPF or Sender ID record for the domain used in your from address, and then you'll need to contact Hotmail about the delivery issue. Neither of these are very fun things to do, especially the latter. But, when you partner with an ESP, they can guide you on how to set up the right SPF or Sender ID record, and they will typically take care of contacting an ISP for you when there's an issue.