Scheduled Emails not being received

[MEM]

Hi All,

I have a client that uses the automated emails in their embedded looker instance. They stopped receiving emails for some reason. I've checked the delivery status in Looker and it shows that it was sent, but the IT department for my client is saying they never hit the server. More interestingly is that some people will get them and other won't at the same client domain. So somehow some of the emails are getting through and some aren't. 

Has anyone ever run into this issue? 

Here are the "job details" on this email with the correct email addresses blacked out, but some went through and others didn't. 

Thanks!