Just went through this process with the Mandrill debacle earlier this year. I've found SendGrid to be on par with Mailgun (with a less wonky admin dashboard too). Both have comparable 10k~12k free sends per month.
If you're using the SMTP gateway instead of direct API integration (which is the only way I'd do it these days, after dealing with a bunch of sites that were tied to Mandrill's API), then there's not really much that needs to happen for the switch.
I just switched to running my software's email from my personal mail server when Mandrill died. Setting up your own mail server is a pain in the ass but it has paid off 100x imo.
I used to send emails from my own servers, with everything configured according to the best practices, as much as I could. This was for account management emails: things like verifying user accounts, resetting passwords, etc.
It seems my emails were getting into spam boxes or outright rejected over 50% of the time, which obviously was driving users away. Mails would sometimes be classified as spam on my own Gmail, even after telling it multiple times to not mark those emails as spam. So I switched to Mailgun, and things have been much more peaceful - sometimes emails take a while to arrive, but I don't remember the last time anyone said it was in spam. It was not about the email content, as the content didn't change...
What's your experience with this? I suppose some domains/TLDs and certain IP address ranges are more prone to be classified as spam than others, and that's why I prefer using an external service: hopefully these guys can control their infrastructure in ways I can't do with mine. But I'm also a supporter of Internet decentralization, and email is one of those things that in principle is easily decentralized...
It takes a lot of upfront work, but I haven't had to do much maintenance on it since the initial setup and my emails get delivered. You have to set up SPF and DKIM, appeal to the blocklists, and set up reverse DNS. Then you have to, you know, not spam people. I highly recommend mail-tester.com, you can send them an email and they'll tell you how to improve it. Here's my score: https://www.mail-tester.com/web-ghs5t5
Thanks, I didn't know about mail-tester.com and similar tools. I am definitely not spamming people, and I had SPF, DKIM and reverse DNS set up, but I don't think I ever did the blocklists part. Something to keep in mind if my projects ever grow too big to fit in the free tiers of Mailgun and similar services.
If you're using the SMTP gateway instead of direct API integration (which is the only way I'd do it these days, after dealing with a bunch of sites that were tied to Mandrill's API), then there's not really much that needs to happen for the switch.