Outbound emails to recipients with a @TelkomSA.net address are not going through to the respective person’s

We are a company trying to send emails to our clients:

It has been brought to our attention that outbound emails to recipients with a @TelkomSA.net address are not going through to the respective person’s.

Call logged with Telkom 29.6.2021(14h43): No reference number was received for this call as they do not give reference numbers. I spoke to Thembisa Pona.

My IT depart investigated this issue : Our systems are fine with no blockers from our end.

When trying to email our customers this is an example of the automated email received: This is the mail system at host smtp-2.ips.emailprivacy.net.

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.

lost connection with mail.telkomsa.net[105.187.200.240] while performing the HELO handshake