Restoring mailboxes from backup duplicates messages in POP clients

[Tanstaafl]

On Wed Apr 10 2019 11:14:29 GMT-0400 (Eastern Standard Time), @lbutlr
via dovecot <dovecot at dovecot.org> wrote:
> On 10 Apr 2019, at 08:59, Tanstaafl via dovecot <dovecot at dovecot.org> wrote:
>> On Wed Apr 10 2019 09:13:41 GMT-0400 (Eastern Standard Time), Luis F. V.
>> Gomes via dovecot <dovecot at dovecot.org> wrote:
>>> I had a disk problem and had to reformat it. All mailboxes were backed 
>>> up using rsync.
>>> After I restored the mailboxes, the POP clients (Thunderbird) that 
>>> were configured to leave the messages on the mailserver for, let's 
>>> say, 30 days, didn't understand that some messages were already 
>>> transfered and the users got duplicated messages in their Inbox.
>>> How can we avoid this?

>> Don't use rsync, use the built in dovecot backup capability?

> Also, don't use POP3?

Well, I can at least understand the argument for someone wanting to use
POP3, but that is beside the point... rsync won't retain the message
UUIDs, while Dovecots backup will, thereby preventing POP3 users
redownloading the emails.