Some BSD systems ship with multiple Berkeley DB implementations.
Normally, Postfix builds with the default DB version that ships
with the system.
To build Postfix on BSD systems with a non-default DB version,
use a variant of the following commands:
% make tidy
% make makefiles CCARGS=-I/usr/include/db3 AUXLIBS=-ldb3
Warning: the file format produced by Berkeley DB version 1 is
not compatible with that of versions 2 and 3 (versions 2 and 3 have
the same format). If you switch between DB versions, then you may
have to rebuild all your Postfix DB files.
Warning: if you use Berkeley DB version 2 or later, do not
enable DB 1.85 compatibility mode. Doing so would break fcntl file
Warning: if you use Perl to manipulate Postfix's Berkeley DB
files, then you need to use the same Berkeley DB version in Perl
as in Postfix.