I came across this in one of the WordPress groups I am a member of and it might be useful to NFP, charities etc.
Mail for Good is a free open source mailing platform from the people over at freeCodeCamp.
For most of us the free MailChimp is fine for our very small mailing lists but if you have more than 2000 people on your mailing list, which isn’t a lot really, then the prices start to stack up, £20 a month just for keeping the list regardless of how many emails you send.
If you use Mail for Good you will need to run it on a server of your own, they say it runs nicely on a £10 a month virtual server and you set it up to use the Amazon Simple Mail Service, there are detailed setup instructions on how to do this. The Amazon Simple Mail Service charges $0.10 per 1000 emails you send. Even without doing any currency conversion if you had a list of 2000 subscribers who you emailed each week it would cost you less than $1 a month.
You can read more about Mail for Good, how to set it up and grab the GitHub link to download it here on the freeCodeCamp page.
My email lists are tiny, a few hundreds of subscribers but I am tempted to give Mail for Good ago just to see how it stacks up against my current platform MailChimp