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The animal on the cover of sendmail, Third Edition is a flying fox, a species of fruit bat found chiefly on the islands of the Malay-Indonesia archipelago. Of about 4,000 species of mammals, nearly one-quarter are bats; and of these, 160 are fruit bats. Sixty of the larger fruit bats make up the flying foxes, the largest having a wingspan of five feet. While smaller insect-eating bats navigate by echolocation, fruit bats depend on a keen sense of sight and smell to perceive their environment. They roost in trees by day, sometimes in extremely large numbers called "camps." They hang from branches by one or both feet, wrap themselves in their wings, and sleep the day away. On hot days, these bats keep cool by fanning themselves with their wings.

Greatly elongated fingers form the main support for the web of skin that has allowed these mammals, to master true flight. At sunset they awaken from their slumber and begin their nocturnal ramblings. A flying fox must flap its wings until it becomes horizontal to the ground before it can let go and fly away. Once airborne, they use their sensitive sense of smell to detect where flowers are blooming or fruits have ripened. Unlike most animals, fruit bats cannot generate vitamin C (a limitation shared by humans and guinea pigs); thus, it is supplied by fruit in the diet. Flying foxes can range up to 40 miles for food. Once a target is located, they are faced with a difficult landing. Sometimes they will simply crash into foliage and grab at what they can; other times, they may attempt to catch a branch with their hind feet as they fly over it and then swing upside down; some will even attempt a difficult half-roll under a branch to grip it in the preferred position. Once attached and hanging, they will draw the flower or fruit to their mouths with a single hind foot or the clawed thumbs at the top of each wing. Awkward landings often cause fights among flying foxes, especially upon their return to camp at dawn. A single bad landing can cause an entire bat-laden tree to become highly agitated, full of fighting and screaming residents.

People have eaten flying foxes for ages. Samoans, who call the flying fox manu lagi (animal of the heavens) use branches bound to the end of long poles to swat the winged delicacy from the sky. Aborigines in Australia build fires beneath flying fox camps-the smoke stupefies the prey-and use boomerangs to knock the creatures to the ground.

Darren Kelly was the production editor, George Jansen was the copyeditor, and Audrey Doyle was the proofreader for sendmail, Third Edition. Mary Brady, Linley Dolby, Matt Hutchinson, and Claire Cloutier provided quality control. Reg Aubry, Julie Hawks, Genevieve d'Entremont, and Judy Hoer provided production support. Brenda Miller updated the index from the second edition.

Edie Freedman designed the cover of this book. The cover image is a 19th-century engraving from the Dover Pictorial Archive. Emma Colby produced the cover layout with QuarkXPress 4.1 using Adobe's ITC Garamond font.

David Futato designed the interior layout. This book was converted to FrameMaker 5.5.6 with a format conversion tool created by Erik Ray, Jason McIntosh, Neil Walls, and Mike Sierra that uses Perl and XML technologies. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSans Mono Condensed. The illustrations that appear in the book were produced by Robert Romano and Jessamyn Read using Macromedia FreeHand 9 and Adobe Photoshop 6. This colophon was written by Michael Kalantarian.

The online edition of this book was created by the Safari production group (John Chodacki, Becki Maisch, and Madeleine Newell) using a set of Frame-to-XML conversion and cleanup tools written and maintained by Erik Ray, Benn Salter, John Chodacki, and Jeff Liggett.