What is best way to create a very large local folder?

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Joined: September 10th, 2017, 3:55 pm

Post Posted September 10th, 2017, 4:20 pm

I'm changing Internet Service Providers, so I need to preserve my existing emails before I make the change.

I'm still using Windows XP. (Yes, I know it's way out of date. I hope to get a new computer soon.)

My current ISP is DSL Extreme and I'm using IMAP with Thunderbird. I'm switching to AT&T and will be using Gmail. I only have a few days before the new service is installed.

I figured an easy way to preserve my existing emails would be to copy them to a local Thunderbird folder. The problem is that I have about 35,000 emails. I've begun trying to delete some of them, but that goes very slow, so I'll still have many thousands.

What's the most practical way to copy them to the local folder without crashing Thunderbird?

Or is there a better way to preserve them?



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Post Posted September 10th, 2017, 8:11 pm

"keep messages for this account on this computer" in the accounts "synchronization and storage" settings should be enabled by default. Unless you explicitly unchecked one of the folders using the adjacent Advanced button, you have a copy of your 35K messages on the PC. That will have created mbox files that contain a copy of the messages for each corresponding remote folder. You can import those mbox files into the Local Folders account using the ImportExportTools add-on. See

The offline folders are not a robust backup though as when you delete a message in the remote folder the corresponding message in the offline folder will be purged. I'd also be leary of counting on those offline folders not getting wiped when you lose access to your DSL EXtreme IMAP server. I suggest you backup your profile and then import the offline folders into "Local Folders" ASAP. They will be safe there when you delete your DSLEXtreme account.

When you are working online TB shows the contents of the remote folders. When you are working offline (via file -> offline -> work offline, not by disconnecting your Internet connection) it shows the contents of the corresponding offline folders, if they exist. If there is no offline folder it shows nothing.

Google imposes a hourly and daily bandwidth limit on uploading/downloading messages to a Gmail IMAP account. Otherwise I'd suggest using a free standalone utility such as IMAPSize to just copy them from one IMAP account to another. See for some other ways to backup your existing accounts messages.

Posts: 2
Joined: September 10th, 2017, 3:55 pm

Post Posted September 11th, 2017, 3:17 pm

Thanks, tanstaafl, for a very complete reply. Please forgive my late response. I just called AT&T and they said my current DSL Extreme email account will not be closed---I will still have access to everything there. So I don't need to archive anything. Hallelujah!

Sorry for the false alarm.

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