How does mail REbuild work?

Thanks. With 25,000 emails (which no longer show the icon for attachements that they used to show for reasons that Apple cannot explain), it is next to be impossible to do that. But I appreciate the suggestion.

I called Apple and spoke with a senior advisor. What he told me is the following:

• Rebuild would not help me. It is used when when messages don't show the content or the content is garbled, etc. That's why all messages in the mailbox are deleted and then uploaded from the server. That's not the problem I am experiencing and for me (due to the fact that I use POP 3) it would not work.
• TimeMachine backs up my mail stored on my computer, including attachments. However, if my mail would get corrupted and I would not notice it quickly to do a restore from the time it got corrupted, by having to go back to an older backup I could loose a lot of data.
• He could not explain the problems I have been experiencing lately with mail.

Unfortunately this didn't solve the problems but at least I know that Rebuild would not be of any help.

Thanks to everyone who tried to help.

Thank you very much for taking the time to provide the advise. I am sorry but I am not really a techie and I am not at all convinced that I could execute what's above. I could try but I am afraid that if something goes wrong I would not know how to fix it.

First I would rather understand if the issues that I am experiencing with mail could be potentially fixed with a Rebuild, once I better understand how Rebuild works. Based on your expert level, if you can address my questions about that, I would very much appreciate it.

Thanks again.

Thanks and I appreciate it. However, I am still hopeful that someone can provide reliable info to address my questions about Rebuild. The performance is not an issue. "Strange" mail behavior is the problem.

Thanks for trying to help.

As I mentioned, I cannot afford to loose neither mail nor attachments. ALL my mail and the attachments are only on my computer. They CANNOT be restored from the provider's server (as assumed in the guide). As a result, not understanding how Rebuild works, what exactly it does, what happens as it "fixes" whatever it fixes, I am afraid to just push the button to experiment even with one mailbox. What if it doesn't act only on the selected mailbox and it deletes all my messages in all maiboxes?

I do not know how Timemachine works either. Would Timemachine be able to restore all my emails with attachments if Rebuild deleted all of them (knowing that they cannot be restored from the server as they are not there)?

I didn't see mail missing or garbled.

I have 4 Mac mail accounts, each with their individual mail addresses and logons. My high level Inbox has a subordinate inbox for each of these accounts. Until now, I could see every incoming mail in the high level inbox and also in the sub-inbox for the respective account. Now, only some show up in the appropriate sub-inbox. Also as I mentioned, periodically the flag decides to show only the spelled out color (not the red picture of the flag but the word "RED").

Obviously this worries me. In addition, not knowing how Rebuild works, I have no idea if Rebuild would fix the issues that I am noticing and as a result I do not know what to do.

If I knew 100% sure that Rebuild would work only on the selected mailbox, as I mentioned, I would move all my mail from my Inbox to a temporary mailbox, run Rebuild on the Inbox and then move the emails back. I have no idea if REbuild would help on an empty inbox and if it would "fix" the issues I am experiencing now.

I was hoping that maybe someone understands how REbuild really works, what it can fix and how it does that and the implications of using it to someone who uses POP 3 and has all emails with their attachments stored ONLY on the Mac.

Well, I have thousands of messages with attachments, some more important than others. While saving them individually might be "safer", it is really not an option for me at this time. This unfortunately is neither a solution to the problem nor an answer about how Rebuild or TimeMachine work. Thanks regardless.

Thanks. I assume Timemachine does its job, but I do not know if it saves all mail attachments, etc. and nobody seems to know...

Thanks. As I mentioned I am not looking for saving options, I am looking for understanding how Rebuild works and if Timemachine backsup/restores all mail with all attachments.