The virus in question passed through our filtering system and was not detected at the time of its passage by our various antivirus engines (ESET, DrWeb, ClamAV, etc.) which are updated every ten minutes. This is a rare case of a virus that was unknown to international antiviral services at the time you received it, probably because it was just created.
You were among the first recipients of this virus attack, which is impossible to avoid by AntiVirus systems (which work by learning), both in filtering and locally on the computer.
You can test the detection of a threat by the main antivirus software on the market by sending the file or link you are unsure about to VirusTotal: https://www.virustotal.com. We also invite you to block executable files (.EXE, .js, etc.) in the administration console in order to reinforce the security of your Mailboxes.