The current list of IP ranges that Luminate Online uses for outbound mail are:
Luminate Online attaches the domain outboundmail.convio.net to the outbound IP addresses that are used. If you have the option to whitelist a sender domain, whitelisting outboundmail.convio.net will allow the delivery.
Note, these IPs are in CIDR notation. For information on CIDR, see this wikipedia page.