Does anyone have advice/recommendations/warnings about email newsletter services? We are currently using a bulk-email module in our CMS (MySource) to send out our monthly "Artmail" and weekly "Art After Hours" update, plus other, less frequent emails. However, this puts quite a strain on our server when each email is sent out and opened (we have a very large subscriber base!). So, I am now investigating 3 bulk email services: PatronMail, Vertical Response and MailChimp. Have any of you used one of these? What kind of experience have you had? Or do you use another solution that might be even better?