Why does T'Bird always have to rebuild summary files?
Every time I do a search on my local folders I find that T'Bird is always "building summary file" for many of my local folders. Is there a reason why T'Bird only does this for some but not all of the folders?
Opaite Mbohovái (1)
If there are often many changes in the folders (adding or removing messages), that will affect how often the folder need to be re-indexed.
Also, the more messages in the folders, the longer it takes to re-index them.
Thousands of messages in a folder that gets new e-mails in all the time = Frequent, long re-indexing.
That is generally the answer to your question.
Here are some tips to keep Thunderbird working well: Keep it working - Thunderbird
I would also add to that:
1. Avoid keeping too many messages in any one folder, just in case the file for that folder on the hard drive gets corrupted.
2. Run Check Disk regularly. How to run a "Check Disk" in Windows