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I don't manage email systems much but my boss is pretty au fait with such packages and products He says that Campaign Monitor is pretty good and offers what you want Their pricing page is here: https://www.campaignmonitor.com/pricing/ The link to the product that you want is a little tricky to find. You have to scroll down the page and click the link which is part of this text: "Only sending emails occasionally? You can also pay per campaign" Pretty sure this deeplink might work fork you https://www.campaignmonitor.com/pricing/#payg From my colleague: "Campaign Monitor have a pay per campaign plan - £4 + 1p per recipient" Might be worth having a look or contacting them