When downloading large attachments in Thunderbird, it often downloads the attachments in small chunks. For example, if you send an attachment with the size of 1MB, Thunderbird may download the message in 10kb parts. This may result in over 100 seperate requests to the IMAP server. Since hMailServer can't have the entire message in memory all the time (that would require to much memory resources), hMailServer have to open,read,close the file between every fetch.

To override this behaviour,

1) Open the file \Mozilla Thunderbird\defaults\pref\mailnews.js
2) Search for fetch_by_chunks. You should find two occurances of this. Set the value of these two parameters to false instead of true.

After that, restart Thunderbird. On my computer, downloading an attachment is at least 15-20 times faster.

(I've made a post in the Thunderbird forum asking about this)

Nice work! I've always wondered why TB handled attachments so poorly...

Jupp.. Well, there's a lot of improvements that can be done on hMailServer when it comes to IMAP performance. I think I'll implement some of those in 4.2..

I'm wondering if anyone knows.... can this pref be set in prefs.js instead of mailnews.js? I'm thinking a future upgrade would overwrite the mailnews.js file. I've tried it in prefs.js but personally can't tell the difference, and I'm not quite sure how to best test it.

Martin, did you ever get any replies back in the forum? I looked but never found your original post.

How big was the attachment? You should probably have an attachment on around 1 MB to notice the difference. Also, since this may be a bug in Thunderbird, I'm far from sure when or why it happens.

Mozillazine.org is so extremly slow and filled with topics so that it's almost impossible to search and find others with the same problem. Takes me like a minute to do a single search and the another when clicking on each row in the result..

Here's my post. I just added an "anyone?" to bring it top the top..
http://forums.mozillazine.org/viewtopic.php?p=1647414

Ok... I tested with a 3mb file and it appears to me that prefs.js overrides mailnews.js defaults. So that seems to work and it does seem to be quite an improvement!

You're right about mozillazine. Slow as molasses... at times in the past they would shut down searching altogether because the site was so overloaded.

Thunderbird has a ton of features, lots of hidden prefs like the one you found. They really should be documented better I think.

Yupp.. The only place I found that setting documented was in the Netscape documentation.

The forum at mozillazine should have been splitted up in several databases. Running _one_ forum with 1,6 million articles feels a bit overkill.

does it works on tb2?
and on linux? cant find te files mailnews.js

found..on the advanced preferences..

Hi Martin,

thank you so much for this hint! This improves TB imap performance on any imap server.
hMailServer is just the best!

Cheers
Wilhelm