Which of the following practices can make an organization's email system susceptible to mail bombing incidents?

The selected practice makes an organization's email system vulnerable to mail bombing incidents because deleting mass emails without implementing proper control measures does not address the root cause of the problem. When an email bomb occurs—where a user receives an overwhelming volume of emails—simply deleting these messages may lead to critical communications being lost or overlooked. It does not provide a defensive mechanism against future attacks and increases system strain, as the email server continues to process incoming emails without sufficient filtration or protection in place.

In contrast, other practices listed, such as implementing filtering rules for massive emails, can help identify and manage potential email bombs before they overwhelm the system. Increasing mailbox storage limits might seem beneficial, but it could inadvertently encourage more spam or unwanted emails to accumulate. Using a professional email service provider can improve security and reliability, helping to mitigate risks associated with such attacks. Hence, the other choices reflect more proactive measures that focus on prevention and management rather than simply reacting to an attack.