In ~/Maildir/cur/ I have: -
1210666181.H610983P31901.203.161.103.17.static.amnet.net.au
           ^^^^^^^       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The Microseconds should start with M.  (Some one needs another X font or
glasses?  Phil, like the old 4.3 code and child.c in particular as this
alone could justify keeping vfork() in Linux.)

The POSIX functions gettimeofday() and getpid() should suffice.

The bit after the second '.' should be from the POSIX gethostname() as
this is short, but unique in an NFS LAN context.  (Replace / with \057
and : with \072.  Also be mindful to replace ' ' with \040 to address
bug #446161.)

The file name and UIDL are longer than they need to be to be unique.
I think that this is a waste of resources.  (If you agree then report
upstream as I their bugzilla has not answered me.)

See Linux man page open(2) and O_EXCL NFSv2 and Linux <2.6.

Maildir as far as MTA delivery is concerned is described in: -
http://cr.yp.to/proto/maildir.html
Unless you are doing something odd with TURN or ETRN plain old
Maildir should suffice.

Functions gettimeofday(), getpid() and gethostname() are POSIX
or SUSv3 so this should be independent of target.  (We really
don't need to care about non-conforming targets do we?)

[...]

This part is fixed in 4.95 (rc0):

JH/01 Bug 1329: Fix format of Maildir-format filenames to match other mail-
      related applications.  Previously an "H" was used where available info
      says that "M" should be, so change to match.

cu Andreas