Agencies often use shared inboxes and mail systems that load images or check links automatically. If several people open the same message, or a scanner does, the signal still belongs to the address you wrote to. Keep the message short: the property reference, when you can view it, and how to reach you.
If there is no reply after a few days, a short polite follow-up or a call works better than more emails. HawkOpen does not write the message or contact the agent for you.