3CX DLL-Sideloading attack: What you need to know
For some time now, some emails that I have been sending from Outlook are bouncing. At the moment an email arrives informing me of the following error: 554 5.7.1 Service unavailable; Sender address [xxx.yyy@xyz.com] blocked using uri.cal1.sophosxl.com Does anyone know how it can be solved?