Fintan
A couple of things to consider about emailing newsletters...
Frequency: not so often is good, you want people to look forward to your newsletter, not filter it into a folder they never look at...
Content: get to the point! The better newsletters leave the content on the website with a hot link to the full article etc. The reader can scan through the titles in the newsletter for example and click down to a summary before deciding whether to go spend time reading the full piece...
Marketing database: if you are a SIG, single interest group, you can email newsletters to your whole database but if you can identify segments, you can distribute based on this and tailor the offering to specific preferences - this is the preferred route even within a given topical field or interest.
Finally, don't overload each newsletter with too many items!
Hope This Helps