[Dovecot] Converting Outlook .PST's

[Benjamin R. Haskell]

On Mon, 15 Oct 2007, Denis Cardon wrote:

> Hi Benjamin,
>> 
>>> [...]
>>> I know the users also have large OUT LOOK pst files 4.5GIGs and wondering 
>>> if 
>>> I could also intergrate that into IMAP?
>> It can be done, but it is a nightmare. For post-2003(?) Outlook .PST's, the 
>> only sensible, non-commercial path I could find was through Thunderbird's 
>> import. Uploading directly to the server (Even if you ran a local server!) 
>> was horrendously, painstakingly slow, and rendered the Outlook user's 
>> computer unusable for that time.
> It is possible to connect outlook directly to an imap server (if it was 
> previously connected to an exchange, you first have to switch it pop/imap 
> mode. I don't remember where you select that). Then you can create a imap 
> connection in addition to the local folders and drag'n drop the mail folders 
> to the new imap connexion. The major issue with this process is when you have 
> a very large amount of folder...

This was the "uploading directly to the server" option I mentioned.

The .PST's we "converted" (using the process I described) were each about 
3 or 4 GB (containing 10-20K messages each). Plus there was an extensive 
folder hierarchy involved (3 top-level folders with about 100 subfolders 
each, and each of those having an average of 3 subfolders -- basically 
/TOP/client-name/job-number).

Our first approach had been to just drag and drop a folder or two (with 
their sub-folders) at a time (totalling ~100MB) at the end of the day, so 
that they'd finish by the next morning. But, there were lots of arbitrary 
errors, making it difficult to both complete the process and to resume 
from errors. (Since the folders were created on the server side, trying to 
resume resulted in "Folder already exists"-type errors.)

In testing, our external server, which we accessed via ADSL at a pretty 
consistent 300Kbps, had about the same transfer rate and characteristics 
as a server I set up on the local (wired, very fast) LAN. Even on the LAN, 
Outlook was taking horribly long amounts of time to transfer. At one 
point, a back-of-the-envelope calculation put the estimate at about two 
weeks (based on what had made it over to the server). And that was for a 
single .PST on a decently fast network (total transfer time for that .PST 
file itself would've been around 8 hours).

I suspect the culprit is Microsoft's less-than-stellar IMAP support, and 
recommend you avoid it. The Thunderbird route has just as many hurdles 
(It's done through SimpleMAPI, which is a subset of Exchange's MAPI that 
runs locally to a machine), but at least it's computationally tractable 
(in some sense).

Best,
Ben