This is the mail system at host mail.zapf.in. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <info(a)fsan-fhl.de&gt;: Host or domain name not found. Name service error for name=fsan-fhl.de type=AAAA: Host not found <arne.krause(a)asta-giessen.de&gt;: host astagiessen-de01b.mail.protection.outlook.com[104.47.51.138] said: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [DBAEUR03FT056.eop-EUR03.prod.protection.outlook.com 2023-06-11T11:05:26.762Z 08DB69A5901A0EFA] (in reply to RCPT TO command) <david.weiler(a)stud.ph-gmuend.de&gt;: host mx1.belwue.de[129.143.76.2] said: 577 5.1.1 <david.weiler(a)stud.ph-gmuend.de&gt;: Recipient address rejected: undeliverable address: host mail-hub02.belwue.de[129.143.76.42] said: 577 5.1.1 <david.weiler(a)stud.ph-gmuend.de&gt;: Recipient address rejected: undeliverable address: host mta-in-vm.ph-freiburg.de[193.197.136.98] said: 550 5.1.1 <david.weiler(a)stud.ph-gmuend.de&gt;: Recipient address rejected: User unknown in relay recipient table (in reply to RCPT TO command) (in reply to RCPT TO command) (in reply to RCPT TO command) <lak-hh(a)asta.haw-hamburg.de&gt;: host b2601.mx.srv.dfn.de[194.95.235.27] said: 550 5.1.1 <lak-hh(a)asta.haw-hamburg.de&gt;: Recipient address rejected: undeliverable address: host mailgate.asta.haw-hamburg.de[141.22.212.2] said: 550 5.1.1 <lak-hh(a)asta.haw-hamburg.de&gt;: Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command) (in reply to RCPT TO command) <fsil(a)uni-hildesheim.de&gt;: host robin.uni-hildesheim.de[147.172.16.6] said: 550 Invalid Recipient 6 (in reply to RCPT TO command)