разобрался, сама BSD клеит общее положение с наличием всех начальных слешей, и их три в итоге, а POSTFIX через virtual.Вот эта часть мануала нам говорит об этом
MAILBOX LOCATION
The mailbox location is controlled by the virtual_mail-
box_base and virtual_mailbox_maps configuration parameters
(see below). The virtual_mailbox_maps table is indexed by
the recipient address as described under TABLE SEARCH
ORDER below.
The mailbox pathname is constructed as follows:
$virtual_mailbox_base/$virtual_mailbox_maps(recipient)
where recipient is the full recipient address.
UNIX MAILBOX FORMAT
When the mailbox location does not end in /, the message
is delivered in UNIX mailbox format. This format stores
multiple messages in one textfile.
The virtual(8) delivery agent prepends a "From sender
time_stamp" envelope header to each message, prepends a
Delivered-To: message header with the envelope recipient
address, prepends an X-Original-To: header with the recip-
ient address as given to Postfix, prepends a Return-Path:
message header with the envelope sender address, prepends
a > character to lines beginning with "From ", and appends
an empty line.
The mailbox is locked for exclusive access while delivery
is in progress. In case of problems, an attempt is made to
truncate the mailbox to its original length.
QMAIL MAILDIR FORMAT
When the mailbox location ends in /, the message is deliv-
ered in qmail maildir format. This format stores one mes-
sage per file.
The virtual(8) delivery agent prepends a Delivered-To:
message header with the final envelope recipient address,
prepends an X-Original-To: header with the recipient
address as given to Postfix, and prepends a Return-Path:
message header with the envelope sender address.
By definition, maildir format does not require applica-
tion-level file locking during mail delivery or retrieval.
