All message delivery for Mail Assure global/US/UK/EU/AU/CA/ZA comes from specific IP ranges. To prevent your firewall(s) from restricting mail traffic, make sure the IPs from this range are accepted.
These IP ranges can also be specified as: 184.108.40.206/24, 220.127.116.11/24, 18.104.22.168/24 and 22.214.171.124/24.
If you wish to use the telnet test from the webinterface or use LDAP sync/authentication, you need to authorize the webinterface IP 126.96.36.199 / 2001:978:2:6::20:10
Note - This is not required for SMTP traffic.