.TH EXIM_ID_UPDATE "8" "September 2023" "Utility for one-time down/upgrade of Exim message-id formats"
.SH NAME
exim_id_update \- one-time down/upgrade of Exim message-id formats
.SH DESCRIPTION
Utility for one\-time down/upgrade of Exim message\-id formats
in spool files between format used in 4.96 and earlier and 4.97 and later
versions.  Only the filenames and the first\-line ID tag values
are affected; not message content such as Message\-ID fields.
Only \fB\-H\fR, \fB\-D\fR and \fB\-J\fR files are handled.

.SH SYNOPSIS
.B exim_id_update [\-d | \fB\-u\fR | \fB\-h\fR | \fB\-v]\fR [spooldir]
.SH OPTIONS
.TP
\fB\-d\fR
Downgrade mode
.TP
\fB\-h\fR
This help message
.TP
\fB\-u\fR
Upgrade mode
.TP
\fB\-v\fR
Version
.PP
Exactly one of \fB\-d\fR or \fB\-u\fR must be given.
The spool directory defaults to the build\-time value,
or can be given as a command\-line argument.
.SH BACKGROUND
The internal exim message ID format changed in 4.97:

Change format of the internal ID used for message identification. The old
version only supported 31 bits for a PID element; the new 64 (on systems
which can use Base-62 encoding, which is all currently supported ones
but not Darwin (MacOS) or Cygwin, which have case-insensitive filesystems
and must use Base-36).  The new ID is 23 characters rather than 16, and is
visible in various places - notably logs, message headers, and spool file
names.  Various of the ancillary utilities also have to know the format.

As well as the expanded PID portion, the sub-second part of the time
recorded in the ID is expanded to support finer precision.  Theoretically
this permits a receive rate from a single comms channel of better than the
previous 2000/sec.

The major timestamp part of the ID is not changed; at 6 characters it is
usable until about year 3700.

Updating from previously releases is fully supported: old-format spool
files are still usable, and the utilities support both formats.  New
message will use the new format.  The one hints-DB file type which uses
message-IDs (the transport wait- DB) will be discarded if an old-format ID
is seen; new ones will be built with only new-format IDs.

Optionally, a utility can be used to convert spool files from old to new,
but this is only an efficiency measure not a requirement for operation.

Downgrading from new to old requires running a provided utility, having
first stopped all operations.  This will convert any spool files from new
back to old (losing time-precision and PID information) and remove any
wait- hints databases.

.SH AUTHOR
This manual page was stitched together from help2man output and Exim
changelog entry 4.97 JH/29 by Andreas Metzler <ametzler at debian.org>,
for the Debian GNU/Linux system (but may be used by others).