Emails not getting received

I've have a few reports that emails on some of your forms are not being sent recently. We've verified the emails are not getting sent to SPAM filter. However, I just filled out the form below and received the customer notification. 

Was there a time when your emails were not sending?

https://www.henryscheinvet.com/registration-forms/dea-compliance-form

Hi,

I do not believe there were any outages recently.  There may be a delay in receiving some of them.  How recent were the missing notifications and do you happen to have the addresses?  When can check our logs to see what may have occurred.