Connection Rejected when trying to send an email to [email protected]

Hello

I'm writing this question about a problem we have in our business with some employes customer at Telus.  I'm working in IT, and I have configured our servers to send alert in the form of email to sms (sms gateway). In case of a problem, our servers can send an email to someone that is in "support mode", this person will receive it in the form of an SMS.

Since a few week, some of our support people, customer at Telus, are not receiving those alert send to thier sms gateway (@msg.telus.com) with this error message

onh-imtacaca02 Telus E2SMS Connection Rejected - fYc9p0rpdlT7r - POL103 - see http://www.spamhaus.org/query/ip/xxx.xxx.xxx.xxx SMTP" 0 130

(I have replaced the IP address with x's for security perpose)

After verifying with Spamhaus,  Spamhaus as no issue with the IP address, so why Telus still reject the email?

thanks for your help