A customer reports their mail can send emails but not receive them. A technician arrives on-site to troubleshoot the issue. Which of the following troubleshooting steps should the technician do FIRST?

Identifying changes to the server is a sub-step within the problem identification phase, which has already been initiated by the customer's report before the technician arrived on-site.

CompTIA's structured troubleshooting model begins with identifying the problem, which the customer has already accomplished by reporting that inbound mail is failing while outbound mail works. The technician's first active step on-site is therefore to establish a theory of probable cause - such as a misconfigured DNS MX record, a blocked inbound SMTP port, or a storage quota issue - which then directs all subsequent diagnostic actions.

Escalating to a manager is premature because no troubleshooting steps have been attempted yet and the complexity or scope of the issue has not been determined.

Root cause analysis is a post-resolution activity performed after the problem has been fixed, not an initial step in active troubleshooting.