How to migrate emails to a secondary imap server preserving folder structure

The subject line could also read: "how to setup an email archiving system that preserves folder structure and tags".

I am reaching the quota of my main email provider (imap1) and I would like to regularly move/migrate some emails to another imap server (imap2) that provides more space.

However it took a lot of time to organize my emails into folders and labels in imap1, and I would like to preserve the folder structure after migration to imap2, so that I can easily locate emails in the archive server imap2.

I found no easy way to do this with mode email clients in MacOS X (Apple Mail, PostBox, Thunderbird, Outlook, ...). The windows version of Microsoft Outlook used to have that feature when archiving to an exteal PST file, but the mac version of Outlook does not seem to support neither PST files nor archiving.

Any ideas would be welcome.

Best regards,

AA

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