sendmail, 4th Edition

Verify Mode (-bv)

A handy tool for checking aliases is the -bv command-line switch. It causes sendmail to recursively look up an alias and report the ultimate real name that it found.

To illustrate, consider the following aliases file:

animals:      farmanimals,wildanimals
bill-eats:    redmeat
birds:        farmbirds,wildbirds
bob-eats:     seafood,whitemeat
farmanimals:  pig,cow
farmbirds:    chicken,turkey
fish:         cod,tuna
redmeat:      animals
seafood:      fish,shellfish
shellfish:    crab,lobster
ted-eats:     bob-eats,bill-eats
whitemeat:    birds
wildanimals:  deer,boar
wildbirds:    quail

Although you can figure out what the name ted-eats ultimately expands to, it is far easier to have sendmail do it for you. By using sendmail, you have the added advantage of being assured accuracy, which is especially important in large and complex aliases files.

In addition to expanding aliases, the -bv switch performs another important function. It verifies whether the expanded aliases are, in fact, deliverable. Consider the following one-line aliases file:

root:       fred,larry

Assume that the user fred is the system administrator and has an account on the local machine. The user larry, however, has left, and his account has been removed. You can run sendmail with the -bv switch to find out whether both names are valid:

% /usr/lib/sendmail -bv root

This tells sendmail to verify the name root from the aliases file. Because larry (one of root’s aliases) doesn’t exist, the output produced looks like this:

larry... User unknown fred... deliverable: ...