Dominque, Have you read this Microsoft guidance on email servers? It covers the most common problems, such as missing SPF records, incorrect or missing IN-ADDR DNS, etc:
https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx -mel beckman On Apr 27, 2021, at 6:54 AM, Dominque Roux <dominique.r...@ungleich.ch> wrote: Hi All, is there anyone out there who has some experience with the blocking mechanism of Microsofts mail server? We're running a mail server at our company which ends up on their blacklist from time to time and we're wondering if there are some steps we could take in order to prevent this. Cheers, Dominique
