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119 lines
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119 lines
5.0 KiB
Plaintext
#!/bin/cat
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$Id: FAQ.POP3.txt,v 1.6 2022/04/05 13:48:52 gilles Exp gilles $
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This document is also available online at
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https://imapsync.lamiral.info/FAQ.d/
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https://imapsync.lamiral.info/FAQ.d/FAQ.POP3.txt
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=======================================================================
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Imapsync tips about POP3.
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=======================================================================
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Questions answered here are:
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Q. Can I use imapsync to migrate emails from pop3 server to imap server?
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Q. How can I handle those terrible POP-leaving-a-copy users?
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POP-leaving-a-copy clients will download a new copy of all
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their emails after a migration, which is a big pain and
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causes hundreds of support calls.
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=======================================================================
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Q. Can I use imapsync to migrate emails from pop3 server to imap server?
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R1. No, but you can migrate emails from a pop3 server to an imap server
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with the command line tool pop2imap:
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http://linux-france.tk/prj/pop2imap/
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http://linux-france.tk/prj/pop2imap/README
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R2. Yes, sometimes, because many pop3 servers runs in parallel
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with an imap server on exactly the same mailboxes. They serve
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the same INBOX, ie, imap serves INBOX and several other folders,
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pop3 serves only INBOX.
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So have a try with imapsync on the same host1.
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=======================================================================
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Q. How can I handle those terrible POP-leaving-a-copy users?
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POP-leaving-a-copy clients will download a new copy of all
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their emails after a migration, which is a big pain and
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causes hundreds of support calls.
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R1. Context and condition: you have access to the POP email client tool
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and the user WILL STAY using POP.
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POP email client tools can leave or delete the messages after pulling
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them. It's very often a configurable behavior. Configure the email client
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tool to delete the messages already pulled and then they won't never
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be pulled again from the server to the client.
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If you can't access to the POP email client tool, see R2 below.
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Problem in the future: INBOX will be seen as empty when the email client
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go to IMAP (unless the email client tool allows then an upload
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synchronization, but don't count on that...)
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R2. Context and condition: you know which users use POP.
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If the pop mailboxes are known then all the INBOX messages can be moved
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in an subfolder called INBOX_backup for example. Ti help you do this,
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the tool pop2imap transfers messages from POP to IMAP, without duplicates,
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without deleting the messages transferred, by default, and can put them
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in any subfolder you want to. It can also delete them and, that way,
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do what the email client tool don't or can't do, for any reason.
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We're here to do a good job with what we have, do we?
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In case of Dovecot for example, the magic can be there since already
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fetched messages via POP are seen as \Seen in IMAP but the new messages are
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seen as new messages, thanks to the Dovecot developper Timo's cleverness!.
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So it is possible to sync back only the new messages to INBOX,
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with "imapsync ... --search UNSEEN ...", and then POP users won't see the old
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messages come back but they will see the new messages and fetch them via POP.
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R3. Context and condition: you know nothing
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Do R2 without the sync back of UNSEEN messages. It can't hurt to have a backup
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of INBOX in a subfolder for IMAP or POP users.
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R4. Here are some points, an analyse that made me purpose the not
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to bad but not very good R2 answer.
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There was a discussion about this issue on the imapsync mailing-list:
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http://linux-france.tk/prj/imapsync_list/msg02622.html
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http://linux-france.tk/prj/imapsync_list/msg02623.html
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My reply was not very good
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http://linux-france.tk/prj/imapsync_list/msg02624.html
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It's because I wrote pop2imap and it uses a stateless
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mechanism to avoid duplicates, I wasn't aware of UIDL when I wrote pop2imap,
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and later when I entered the discussion.
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See also Rick Sanders discussion about this issue:
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https://www.emailquestions.com/threads/how-to-prevent-duplicate-emails-after-server-migration-for-pop3-users-with-leave-mail-on-server.8109/
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Quoting Timo Sirainen on
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https://wiki2.dovecot.org/Migration
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"If a client already saw changed UIDLs and decided to start
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re-downloading mails, it's unlikely there is anything you can do to
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stop it. Even going back to your old server is unlikely to help at
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that point."
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"Some (many?) POP3 clients also require that the message ordering is
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preserved."
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"Some clients re-download all mails if you change the hostname in the
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client configuration. Be aware of this when testing."
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Quoting
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https://wiki.dovecot.org/POP3Server
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"Flag changes
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By default when a message is RETRed, \Seen flag is added to it.
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POP3 itself doesn't support flags, but if the mailbox is opened
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with IMAP (eg. from webmail) it's shown as seen."
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=======================================================================
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=======================================================================
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