Some mailbox file of Lotus Notes (.nsf) is quarantined starting form the end of April 2017

I find that some mailbox file of Lotus Notes (.nsf) is quarantined (Reason: Trojan.Pidief) starting from the end of April 2017, it seens that Endpoint Protection can be scanned the actural content of each mail to identify if the attachment of each email is affected for not.

In our case, we have a specific mailbox to collect such affected email, but that nsf file is identified and quarantined, we don't know the protection to have such behaviour. Also, I would to know if it is related to the patch update or other reason, thx!