The same as if you configure sendmail_oath wrong or move you binary to a
host where it is missing: mail() returns false.
I think it's a correct approach - the fact that sendmail wasn't installed (or installed incorrectly maybe) on build machine shouldn't prevent PHP from sending mail of production machine. If production machine doesn't have sendmail - mail() would fail as would any other function, such as database connection, when environment is not set up correctly.
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Stanislav Malyshev, Zend Software Architect
stas@zend.com http://www.zend.com/
(408)253-8829 MSN: stas@zend.com