Internally, sendmail marks the
recipient george as defunct, having been replaced with an alias, and then adds gw to
the list of recipients.
The new recipient, gw, is then processed for delivery. The canonify rule set 3 and the
parse rule set 0 are called once more and again select a local delivery agent. As a consequence,
gw is also looked up. If it is found to the left of a colon in the aliases file, it
too is replaced with yet another address (or addresses). This process repeats until no
new local addresses are found.
Note that the entry george is marked defunct rather than being deleted to detect alias
loops. To illustrate, consider the following two mutually referencing aliases:
george: gw
gw: george
The sendmail program first replaces george with gw, marking george as defunct. It
goes to mark gw as defunct but notices that a loop has been formed. If sendmail is
running in verbose mode (?§24.9.129 on page 1117), it prints:
aliasing/forwarding loop broken
and bounces the message.
Note also that aliases can get pretty complex. As a consequence, when one address
aliases to many new addresses, this autodetection of loops can fail (but the problem
will be caught later with ???hop counting;??? see ?§24.9.67 on page 1046).
12.1.3 Alias Nonlocal Addresses
As distributed, a normal configuration file will disallow certain addresses on the left
side of the aliases file.
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