Which of the following can be considered a proactive measure in email security?

Regularly updating software and email clients is a proactive measure in email security because it helps to mitigate vulnerabilities that could be exploited by attackers. Keeping systems up-to-date ensures that the latest security patches and improvements are applied, which can prevent unauthorized access and various types of malware infections that often target outdated software. This practice helps to create a more secure environment by addressing potential weaknesses beforehand, rather than reacting to threats after they have already occurred.

In contrast, the other options suggest a reactive approach, where actions are only taken in response to incidents or threats after they have manifested, thereby increasing the risk of damage or loss.