Receiving postmaster delivery failures despite the mail being delivered.

Hi there,

since a few days I receive postmaster delivery errors for mails I send. The person that sends mails to me also receives postmaster errors. However, all the mails are delivered successfully. Does anybody know the problem and maybe the solution?

Below the postmaster messages:

Error message, I receive when sending to others:

Von: postmaster@mac.com
Datum: 4. Mai 2019 um 16:14:51 MESZ
An: ME@icloud.com
Betreff: Delivery Notification: Delivery has failed

This report relates to a message you sent with the following header fields:
[...]

Your message cannot be delivered to the following ..]recipients:

 Recipient address: ME@skynet.be
 Original address: ME@icloud.com
 Reason: SMTP transmission failure has occurred
 Diagnostic code: smtp;554 5.4.0 Error: too many hops
 Remote system: dns;smtpout.mac.com (TCP|17.164.88.128|60416|10.112.110.142|25) (ms11p00im-qufo17291701.me.com 3.3.1 v.666)

Reporting-MTA: dns;ms17512.mac.com (tcp-daemon)
Arrival-date: Sat, 04 May 2019 14:14:51 +0000 (GMT)

Original-recipient: rfc822;ME@icloud.com
Final-recipient: rfc822;ME@skynet.be
Action: failed
Status: 5.4.0 (SMTP transmission failure has occurred)
Remote-MTA: dns;smtpout.mac.com (TCP|17.164.88.128|60416|10.112.110.142|25)
(ms11p00im-qufo17291701.me.com 3.3.1 v.666)
Diagnostic-code: smtp;554 5.4.0 Error: too many hops

Error message, others receive when sending to me:

This report relates to a message you sent with the following header fields:

 [...]

Your message cannot be delivered to the following recipients:

 Recipient address: ME@skynet.be
 Original address: ME@icloud.com
 Reason: SMTP transmission failure has occurred
 Diagnostic code: smtp;554 5.4.0 Error: too many hops
 Remote system: dns;smtpout.mac.com (TCP|17.164.88.128|42383|10.112.94.199|25) (mr85p00im-zteg06021901.me.com 3.3.1 v.666)

Reporting-MTA: dns;ms17512.mac.com (tcp-daemon)
Arrival-date: Tue, 30 Apr 2019 16:28:00 +0000 (GMT)

Original-recipient: rfc822;ME@icloud.com
Final-recipient: rfc822;ME@skynet.be
Action: failed
Status: 5.4.0 (SMTP transmission failure has occurred)
Remote-MTA: dns;smtpout.mac.com (TCP|17.164.88.128|42383|10.112.94.199|25)
(mr85p00im-zteg06021901.me.com 3.3.1 v.666)
Diagnostic-code: smtp;554 5.4.0 Error: too many hops

Thank you!