To find out if your e-mail is in the Inbox, you need to get the label "Incoming Billing". This indicator may be provided by Return Path, but it is quite expensive. If you do not ship huge volumes, this may not be worth it. The only way to measure IPR is to actually have a certain number of test mailboxes ... In other words: the only way to check that your email is not in the spam folder is to do a test and see what happens. There is no other magical solution and what Return Path does.
This means that when you hear about people claiming to have 99% delivery / delivery, maybe it just means that the Internet address has been “received” or “delivered” by the provider. That is a lot, but that’s not all!
What you have to do is this: use ESP's focus on delivery options. Personally, I work at Mailjet. I believe that this is the best value you can get: personalized DKIM and SPF are free, you get spam ratings, analytics, IP reputation monitoring, throttling, etc. It's all in one tool to avoid headaches to optimize yourself. It's more expensive than Amazon SES because you get a lot of additional services, but it has much lower prices than many traditional ESPs!
Bottom line: optimizing everything you work full time. Knowing for sure if an email is in your inbox or not will cost you a lot. Best way to continue:
- follow best practices (choose, not too many images, not red, etc.).
- Get some metrics like open rates, clickthrough rates, delivery, etc. and monitor their evolution over time. Any change from one dispatch to another can be a signal for the problem you want to investigate.
- Use a tool that takes care of all the optimization possibilities.
Mailjet is cool, because no matter what plan you choose, you can use all the options. But if you want a full overview of the existing, see this comparison table:
http://socialcompare.com/en/comparison/transactional-emailing-providers-mailjet-sendgrid-critsend
If you are a perfectionist who wants to refine the layout, how emails are displayed, etc. Check out Litmus, it's also a pretty powerful tool!
http://litmus.com/