I am working on an open source project (it is still in early development), and I am trying to find the best solution for email for the project.
I currently have tried Mailgun and absolutely love it, it is quite fast, informative, and developer friendly. You can, for free, send and receive 10,000 emails a month and validate 100 users.
The problem is I see at least 2 emails required per user that signs up - one to be sent for verification, and one that welcomes the user after verification. This leaves 5,000 users a month that can register and receive emails which, I do not know if I will surpass that or not. On top of this, emails sent to the "support" address will count as an email processed, and after that it leaves very little room for any additional emails.
The site will eventually reach a point where it will involve some sort of monetary system BUT this is to facilitate transactions between users and not to make profit or sell a product. I could take fees from that and also accept donations.
Otherwise for $79 a month Mailgun allows 100,000 emails to be processed and 1,000 user validations. Now that I write this though I do think Mailgun may be pay-as-you-go for its free plan, too...
Is this probably the best way to go, is with Mailgun? Or do you know of any other developer and open-source friendly email solutions?