[Dovecot] dovecot mounts user home dir?

[TM]

Why does dovecot mount the user home directory
whenever the user checks his email (either pop or
imap)?

Is there a way to disable this?

I have indicated in the default_mail_env =
mbox:/home/%u/:INBOX=/mail/%u:INDEX=MEMORY.

The users are in ldap. Windows users' home is in
/home/%u so this is ok but unix users' home are in
their local computers and are mounted (via automount)
at /d1-data/pcname/username.

Even if mounted, the users' home directory isn't used
by dovecot since nothing gets written to it. The users
only checks his pop mail but still, his home directory
gets mounted.

Is it possible that dovecot won't try to mount the
user's home directory whenever the user checks his
mail?

Thanks a lot.

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