Gmail, Yahoo work but iCloud emails bounces with 503 5.5.1 Error: send HELO/EHLO first (in reply to RCPT TO command)

1

This is the mail system at host mail.domain.tld.

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

<recipient@icloud.com>: host mx01.mail.icloud.com[17.57.155.25] said: 503 5.5.1
Error: send HELO/EHLO first (in reply to RCPT TO command)

Reporting-MTA: dns; mail.domain.tld
X-Postfix-Queue-ID: 7CF86895CC
X-Postfix-Sender: rfc822; support@domain.tld
Arrival-Date: Tue, 1 Apr 2025 06:57:55 +0000 (UTC)

Final-Recipient: rfc822; recipient@icloud.com
Original-Recipient: rfc822;recipient@icloud.com
Action: failed
Status: 5.5.1
Remote-MTA: dns; mx01.mail.icloud.com
Diagnostic-Code: smtp; 503 5.5.1 Error: send HELO/EHLO first

2

This problem can be caused by a missing PTR record. Do you have your reverse DNS set correctly? What does the status checks page say?

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3

You can test via telnet.

SSH to your box and send test email to a real icloud recipient.

Read here: How to Test an SMTP Server with Telnet. Step-by-Step Tutorial

telnet mx01.mail.icloud.com
Or tail the mail log when sending from MIAB and paste here the response:

cat /var/log/mail.log | grep "postfix/smtp" | grep -P 'status='

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