dovecot migration

[mkawada at redhat.com]

Dear List,

To migrate a dovecot server from dovecot-1.x to dovecot-2.x, then I
wonder if the UIDL format "pop3_uidl_format" setting is required in the
configuration file for clients not to re-download the same mails from
the migrated mail server. Currently, no UIDL format is set in
/etc/dovecot file of the one using dovecot-1.x server which means it is
commented out as default like below.

]# grep pop3_uidl_format /etc/dovecot.conf

#pop3_uidl_format = %08Xu%08Xv <----

Does this mean the "pop3_uidl_format" is in use as "%08Xu%08Xv" by
default? I see the same in /etc/dovecot/conf.d/20-imap.conf of the one
using dovecot-2.x, and have not been able to find any information saying
it's the defualt setting.

Here are the questions:

1.Can we say the "pop3_uidl_format = %08Xu%08Xv" is the enabled default
setting? Or any ways to check the default?

2.Do they need to specify anything for the "pop3_uidl_format =" field
for their migration in this case?

Env infomation:
dovecot-1.x
dovecot-2.x
mail_location = mbox

Any information/clues would be greatly appreciated.

Thanks,