When sending an internal email to a colleague, you could get an error message: ‘Your message has been delayed for some or all of the intended recipients.’ Or it might be possible that the email does not arrive at the receivers end.
It could be helpful to ask your IT department to whitelist the IP addresses below:
109.68.163.0/26
109.68.163.128/26
109.68.163.192/26
109.68.167.96/27
A large chunk of our traffic comes over 1 IP address: 109.68.163.183 (109.68.163.183/32)