Exchange Server receives mail but not delivered to mailbox

We use Barracuda Essentials for anti-spam and it receives all incoming email and hands off valid ones to our on-premise 2016 Exchange Server.  It is working fine except for one external account that shows the email being accepted by our exchange server but it never makes it to the intended user's inbox.  When I do searches using Get-MessageTrackingLog - sender [external email account that isn't working] then there is no response other than a blank line which indicates no emails were received.  I checked the event logs and there where no events that appear to be related, error or otherwise.