It happens to all of us from time to time that Outlook sometimes misjudges an email message and puts it in junk mail, even though it is not junk.
You can improve the quality of mail filtering in a few steps. The first is to disable the so-called local spam filter in Outlook - the mail filtering is then handled only by the mail servers, whose settings are continuously updated and thus evaluate the emails more accurately than the local filter.
On office computers and laptops in central administration (you log in with a user ID and a secondary password), we have disabled the local spam filter across the board. If you also use Outlook on a non-centrally managed computer or laptop, you must manually disable the local filter on each such computer - see the instructions for setting/deactivating the local filter (Czech only) on the MUNI IT website.
At the same time, we recommend that you have work computers and laptops owned by FF transferred to central management - this will greatly simplify the setup of this type for you and us; you will not have to worry about updating the operating system and centrally maintained programs, you can comfortably work with the same tools in the same configuration on multiple devices at the same time, etc. Discuss the transfer to the domain with your technician or make a request directly.
The second important step for more accurate mail filtering is to manually mark incorrectly detected junk messages as correct. This can be done by following the instructions on How to report a correct message in Outlook. Equally important is marking spam or phishing emails that arrive in your inbox when they should have ended up in spam - manually mark the message by following the How to Report Unrecognized Spam and How to Report Unrecognized Phishing Messages instructions.
Mail administrators in O365 continuously monitor user reports. If there is a larger wave of spam/phishing emails, they can take additional measures based on the larger number of such reports, e.g. remove malicious messages from mailboxes after delivery.