LPIC-2 DNS, Web and Mail Services Practice Question
A Postfix mail server is configured to use Dovecot SASL for authentication. Users report that they can send emails but are prompted for password repeatedly and see "SASL authentication failed" in the logs. The Dovecot SASL socket is configured correctly. What is the most likely cause?
⚠ Common exam trap
The trap here is that candidates often focus on authentication mechanism mismatches or network-level settings, overlooking the fundamental Unix permission issue on the SASL socket, which is a classic gotcha in Postfix-Dovecot integration.
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 postfix user does not have permission to access the Dovecot auth socket.
The most common cause of repeated password prompts and 'SASL authentication failed' errors when Postfix is configured to use Dovecot SASL is a permissions issue on the Dovecot auth socket. Even if the socket path is correct in Postfix's `smtpd_sasl_path`, the Postfix process (typically running as the `postfix` user) must have read/write access to that socket file. Without proper permissions, Postfix cannot communicate with Dovecot's authentication service, causing SASL failures despite correct authentication mechanisms and enabled settings.
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 mynetworks parameter in Postfix is set to the wrong subnet.
Why it's wrong here
mynetworks controls relaying, not SASL authentication.
- ✓
The postfix user does not have permission to access the Dovecot auth socket.
Why this is correct
Permission issues prevent SASL communication, causing authentication failures.
- ✗
The Dovecot auth mechanism is set to 'login' but Postfix expects 'PLAIN'.
Why it's wrong here
Postfix can negotiate mechanisms; a mismatch would cause a different error.
- ✗
The smtpd_sasl_auth_enable parameter is set to no.
Why it's wrong here
If disabled, no authentication would be offered.
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JA
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.