Stormpath is agnostic to the the type of SMTP provider that you choose to use for your tenant. However a few SMTP providers require that you do custom changes for the client (Stormpath in this case) to get things working. We've tested this with multiple providers and out of these the ones that need custom work are: Office365, Google G-Suite, and AWS.
For reference, here's the documentation
1. Collect your Office 365 credentials using this guide.
2. Configure your SMTP server on Stormpath following this guide along with the credentials from step 1.
3. Office365 requires that the sender address on the client should match the username with you configure with on Stormpath. For example, if my admin Office365 username is firstname.lastname@example.org, the sender email in my Stormpath directory should be email@example.com.
4. Go to the directories tab on the admin console, click on your users directory, go to workflows, and under sender email, change that to the username of your Office365 account.
G-Suite treats any third-party applications as 'unsecure-clients.' Follow this guide about allowing 'unsecure-clients' to use your SMTP server. We tested this to work with TLS and smtp.gmail.com on port 587.
We've had situation where a few customers using AWS SMTP server weren't able to send messages. This could be due to various reasons. Make sure your network is not blocking outbound connections over the port you're trying to send email from. Try the following command: telnet email-smtp.us-west-2.amazonaws.com <port>, where <port> is the port you're trying to use (typically 25, 465, 587, 2465, or 2587).
If that works, and you are trying to connect to Amazon SES using TLS Wrapper or STARTTLS, try the openssl commands shown in Using the Command Line to Send Email Through the Amazon SES SMTP Interface. If you cannot connect to the Amazon SES SMTP endpoint using telnet or openssl, then something in your network (for example, a firewall) is blocking outbound connections over the port you're trying to use. Work with your network administrator to diagnose and fix the problem.
If you are using some other SMTP server and are running into issues, please reach out to us: firstname.lastname@example.org