firewall problem sending from btinternet domain to a company is South Africa

[haltokeit]

I am trying to send an email to a company in South Africa from my btinternet account. The mail server has returned the following message. I have removed the actual name and email address that I am trying to send to.
- These recipients of your message have been processed by the mail server: xxxxx@xxx.co.za
; Failed; 5.5.0 (other or undefined protocol status)

    Remote MTA relay2.ncc.co.za: SMTP diagnostic: 554 5.7.1 Firewall: E-mail firewall rules determined that the domain btinternet.com is not allowed to send e-mail to (*)xxx@xxx.co.za.
This appears to be an issue with the recipient's firewall, is that correct? I have successfully sent an email to the same address using gmail. Can anyone advise me how to resolve the problem?
Thanks.

[naylor2006]

The error relates to the recipient mail server, maybe they have reputational based rules and somehow BT's domain has got mixed up in that, or it could be geo based stuff also but less likely because its coming from the UK.

Most simply they can whitelist you rather than adjust any other automatic firewall rule that may be working on some other metric.

[haltokeit]

Thanks naylor2006. That confirms what I thought.