To prevent service abuse and spam, The Messaging Company limits the amount of emails that can be sent when a customer has not configured outgoing authentication in their email application.

If you receive a rejection or error message such as "Throttled due to Sender Policy - Please try again later" This indicates that you are sending a large number of emails in a short period OR your email settings do not have outgoing mail authentication.

Option 1

We highly recommend updating your outgoing email settings to 1) Use IMAP, 2) Set the outgoing mail server settings as per this article: Mail Server Settings

If you are not familiar with modifying server settings, it is suggested you remove your email account from your mail application and set it up by following the relevant article for your chosen email application. 

I want to access my email using a mail app

Option 2

You may continue to use the existing settings, however restrictions will apply on the volume of emails you are able to send.  If you receive a throttling error message, you will need to wait and resend the email at a later time.