What transacional email service are you using?

What transacional email service are you using?

  
Sending an email is one thing making sure it lands on the inbox is other. We are struggling with the second. 

We are looking for services like mailgun and mandril. What transaconal email service are you using with your OutSystems web platforms or apps and why? 
Solution
I have used Mandrill, and I liked it a lot. Used it because we already had a Mailchimp intgration and it was natural to go to Mandrill. At first we just used it for SMTP and it was fine, later shifted to using it through the API; I left the project before that project went live, but the integration was pretty easy and it supported everything we needed.

J.Ja?
Solution
Thank you Justin. Very useful. We will compare mandril and mailgun. We will try to test them through the API and see if we do well integration-wise. If anyone else have thoughts on this please share :) Cheers! Hugo
With mandrill you need to have an active mailchimp subscription (it use to be that you can signup and use mandrill as a standalone product, not anymore!)

Mandril is a good product, but if your not going to be creating newsletters and just want a stand alone SMTP solution go with sendgrid or even amazon ses! (UI can do with a little work but it works and works well).
Thank you Robert!
We use sendgrid, and it easily tracks links if you are using their whitelabel version out of Outsystems, we do a lot of landing pages, we will probably use there API into Outsystems in the next few months.
I used Mandrill before it went to a pay model, and since have switched to Mailgun.  Everything has worked perfectly..
@Adam you are using Mailchimp the API or the SMTP way? 
SMTP
FYI, 94% delivery success with Mailgun