Autodir is a modular daemon for creating directories transparently, based on autofs.
It is a thread-enabled tool to create and/or mounting and managing automagically and transparently user/group home directories, on demand. It can work with any authentication framework (e.g. system files, NIS, LDAP or SQL) and does not require PAM, which is a required feature for session-less service such as email servers.
Automounter version 4 (autofs4) has to be enabled when compiling the kernel. Debian packaged kernels have it enabled as module.
For more information, consult online docs at https://tldp.org/HOWTO/html_single/Autodir-HOWTO/index.html or the up-to-date version under the doc/ directory.