If you placed the messages in Local Folders, they will stay. If they are in message folders for an IMAP account, they will be lost. Please provide more detail to 'imported several years of emails to TB' to ensure I'm giving correct information for your situation,

I closed the reply started as a new thread here https://support.mozilla.org/en-US/questions/1472992

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I did not make myself clear. I forward email from Comcast.net to Outlook 2010 in IMAP format. Email is in multiple directories. I pulled email from Outlook 2010 (I think) into TB. If I cancel Comcast, will it delete the email I stored in TB? It removes email in Outlook if I cancel the update link from Outlook to pull from Comcast. Can I continue to read and respond to old email using TB? Thank you

I imported several years of emails from my comcast.net account to TB. I plan on canceling Comcast completely. Will the emails I imported remain in TB or will they disappear? I tried this in Outlook and all of my old emails disappeared. I can't afford to lose some old very important emails

This is just too ridiculous to understand. you are not simple to understand. I uninstalled Thunderbird as no good

@Maursie. You are quoting yourself and saying it is to difficult to understand. I agree it is difficult.

You need to understand that email is not email. It is IMAP email or POP email or even Exchange email as well as some other corporate flavours. Therefore there is no simple response to your simple question because your question is not simple.

If you account is configured as IMAP in a mail client. Any mail client then the local mail you see if syncronised to the mail server and it will be lost as soon as the mail server account is lost.

If your account is configured as POP then the mail is downloaded, not syncronised. But this process only included the inbox for the mail account not the plethora of other folders as with IMAP.

Should your account be one of the other non standards based protocols then another set of constraints will probably exist for that.

So I concur, until you have a better understanding of email protocols you probably should not be using an offline mail client to archive emails.