FortiMail causing all domain users to be locked out

Hi there,

One of our clients has recently noticed an issue where all of their user accounts were attempted to be logged on to and then locked out from the FortiMail source IP address. 

It appears to be an intermittent issue, and we've yet to be able to determine the cause of it. Just wondering if anyone else has experienced something similar? And if so, what was done to resolve the issue?

Kind regards,

Mark