FYI it was a Microsoft O365 configuration issue, indeed. In our hybrid environment (O365 + Postfix) a routing configuration that is commonly enabled in O365 (called "inbound connector") generated that loop. After a few weeks of mail exchanges with Microsoft support they gave us the solution. If you want to know more about O365 mail routing, they sent me this article: https://techcommunity.microsoft.com/t5/exchange-team-blog/office-365-message-attribution/ba-p/749143 . Thank you for your help and have a nice day.
Il giorno gio 19 mar 2020 alle ore 12:20 Wietse Venema <wie...@porcupine.org> ha scritto: > > > > 14 times > > > db8p195mb0565dd65da92d1861c8946u48c...@db8p195mb0565.eurp222.prod.outlook.com > > > 14 times > > > vi1p195mb02560627a8aa5227c95208cd80...@vi1p195mb0256.eurp222.prod.outlook.com > > > 14 times > > > vi1p195mb0463506au7u3dc47au795a8u92...@vi1p195mb0463.eurp222.prod.outlook.com > > > > That proves that email is really going back and forth between > > your site and Microsoft. > > > > > I think I'll try with Dusan advice and let you know. Feel free to > > > suggest something else if comes to your mind. > > > > DO NOT STRIP Received: headers. THAT WOULD BE A HUGE MISTAKE. > > Where should the above email be delivered? MICROSOFT or POSTFIX? > > - If this email should be delivered at MICROSOFT, configure MICROSOFT > so that it does not forward this email to POSTFIX > > - If this email should be delivered at POSTFIX, configure POSTFIX > so that it does not forward this email to MICROSOFT.
