I didn't read the info in Whiskeyman's link but on my system (XP-SP2
) it never asks, it just goes ahead. I have read somewhere that after each hundred sessions, when you close down OE, the folders get compacted. I can still do a manual compacting of individual or all folders.
Things have gone wrong (for other people, not me personally) when compacting and one of the dangers is to get incoming mail while the compacting is being processed. That's why they changed the automated compacting to occur when OE gets shut down (every hundredth time). OE keeps track of the sessions in a specific registry key. The "counter" can be reset to zero to avoid compacting. However, after some time, if the folders aren't compacted other problems (corruption) may show their ugly faces when the size grows.
I don't have a lot of important E-mails and I wouldn't cry if I lose them but I backup the E-mail folder on a regular basis (each month at least). If something should go wrong, I only have to copy the backup files back to the original location and most E-mails, apart from the most recent ones, would be safe.
I let it do the automated compacting and when I do a manual, I always block traffic in the FireWall to prevent incoming E-mail.