LPIC-2 DNS, Web and Mail Services Practice Question
A company runs a Postfix mail server that relays mail for internal clients. Users report that emails to a specific external domain 'example.org' are delayed by several hours. The administrator checks the mail logs and sees entries like: 'status=deferred (connect to mx.example.org[203.0.113.10]:25: Connection timed out)'. What is the most likely cause?
⚠ Common exam trap
Candidates often confuse 'deferred' with a relay authorization issue or a DNS problem, but the specific 'Connection timed out' error points to a network-layer block rather than an SMTP-level rejection or misconfiguration.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The remote mail server mx.example.org is blocking connections from the company's mail server IP.
The log entry 'Connection timed out' indicates that the company's Postfix server successfully resolved the MX record for example.org to the IP 203.0.113.10 but could not establish a TCP connection to port 25 on that host. This is consistent with the remote server explicitly blocking inbound connections from the company's IP, often via a firewall rule or access control list, rather than a DNS or rate-limiting issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The company's mail server is not authorized to relay mail for the internal clients, causing a deferral.
Why it's wrong here
Relay authorization failures produce 'Relay access denied' errors, not connection timeouts.
- ✗
The DNS MX record for example.org is misconfigured, pointing to a non-existent host.
Why it's wrong here
If MX record pointed to non-existent host, Postfix would get a DNS resolution failure, not a connection timeout.
- ✓
The remote mail server mx.example.org is blocking connections from the company's mail server IP.
Why this is correct
Connection timed out suggests the remote server is not responding, often due to firewall or server issues.
- ✗
The remote server is rate limiting connections from the company's mail server.
Why it's wrong here
Rate limiting typically produces a temporary failure after connection is established, not a timeout.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-2 practice question is part of Courseiva's free LPI certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LPIC-2 exam.