sendmail, 4th Edition

implicit

Search for an aliases database entry V8.1 and later

The implicit database-map type refers specifically to aliases(5) files only. It causes sendmail to first try to open a db(3) hash-style alias file. If that fails or if NEWDB support was not compiled in, it tries to open an ndbm(3)-style database. If that fails, sendmail reads the aliases(5) source file into its internal symbol table.

When sendmail rebuilds its aliases database (as with newaliases) it looks for the special string literal /yp/ anywhere in the path specified for the aliases source file. If that string literal is found, sendmail uses this implicit type to create both a db(3) hash-style alias file, and an ndbm(3)-style database. It creates both to support NIS compatibility.

Although you can declare and use this type in a configuration file, there is no reason to do so. It is of use only to the internals of sendmail. If implicit fails to open an aliases file, probably because of a faulty AliasFile option (AliasFile on page 970), sendmail will issue the following error if it is running in verbose mode:

WARNING: cannot open alias database bad filename

If the source aliases file exists but no database form exists, sendmail will read that source file into its internal symbol table using the stab type (stab on page 938).

You can experiment with this implicit database-map type using a mini configuration file such as this:

V10
Kxlate implicit -a.Yes -o /etc/mail/aliases
Stest
R$*     $: $(xlate $1 $)

Here, we declare a database ...