Mailing List In Thunderbird

Any Mozilla Thunderbird experts out there?
I have transferred my POP mail server infor (incoming and outgoing) into Thunderbird. Sending mail and receiving new mail is not a problem, but it’s not listing what was in my inbox before the transfer. Why? Is this just not possible?
On the previous email client. have you configured the settings to leave a copy of messages on server. In that case even if you transfer from one email client to another you still can download the previous emails.
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