Here are some easy steps you can follow to ensure that you're using Dotdigital's transactional email service correctly and all is working as expected.
Checking enablement and sending
Firstly, before you have enabled transactional email in Magento, you will want to ensure the functionality is enabled on your Dotdigital account. You can do so by logging into your account, mousing over the dropdown menu next to the Dotdigital logo in the top left-hand corner and selecting Transactional email. Upon arriving at this page you should be presented with a reporting dashboard. If you are presented with a pop-up window to purchase the feature, then it is not yet enabled on your account.
If you have confirmed this is working and you have enabled transactional email within Magento, you should start seeing emails being reported within your Dotdigital account.
If the frequency of transactional emails is not significant on your site, then it is always worth testing some of the basic transactional emails yourself, such as registering for an account or submitting a forgotten password request.
I have the feature enabled in my Dotdigital account and in Magento but no transactional emails are showing and I'm not receiving my tests. What's wrong?
This could be due to one of the following reasons:
1) Your SMTP credentials are incorrect. Please double-check this.
2) The port selected in your 'Transactional Emails' settings is not allowed on your website's server. Please test the others that are available for selection.
3) You may have another email extension conflicting with ours. Please review and disable other extensions you may think could be causing an issue.
Please comment underneath with any further questions you may have.
The above also applies for Magento 2.0, with the only difference being that the 'Transactional Emails' section is found by going to Stores > Configuration > DOTMAILER > Transactional Emails.