/etc/aliases contains the line `dave: dave@newjob.example.com`, and at the same time ~dave/.forward on the server contains `\dave`. Mail arrives for dave@thishost. What happens?
LPIC-1 Exam 102-500, objective 108. Essential system services hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct The message goes only to dave@newjob.example.com; the .forward file is never consulted
Correct. Alias expansion happens first and rewrites the recipient to a remote address. Once the recipient is no longer a local user on this host there is no home directory to look in, so the .forward file plays no part.
Not correct The message is delivered only to the local mailbox, because a user's .forward overrides a system alias
Wrong. Precedence runs the other way: the system aliases database is consulted by the delivery agent before any per-user file, and a user cannot reclaim an address that an alias has already redirected.
Not correct The message is delivered twice, once locally and once to the remote address
Wrong. Two copies would require two destinations in one expansion, for example both addresses listed on the right-hand side of the alias. Here the alias yields exactly one recipient.
Not correct The message bounces with a forwarding loop error
Wrong. A loop needs an expansion that returns to itself. The alias resolves to a remote address in one step and the backslash in the .forward file would in any case terminate expansion rather than continue it.
Why
The local delivery agent resolves a recipient in a fixed order: the aliases database first, then the recipient's ~/.forward file, then the mailbox itself. Because aliasing runs first and can send the address off-host, only an administrator can decide whether a name is delivered locally at all; a user's .forward can redirect their own mail but cannot pull back an address the alias has already claimed. To keep a local copy as well, the alias itself must list both destinations.
Where this comes from
- Cited
- manual page local(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 108 and space the ones you get wrong.
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