dovecot - Oct 2005 - Changing pop3_uidl_format

I recently set up an OpenBSD - Dovecot mail server for a client. Naturally 
(according to Murphy's Law) they want to use Outlook 2003, pop3s, and leave 
messages on the server. And just as naturally, the UIDLs don't seem to be 
working, and when they download mail, they get EVERY email stored on the 
server, not just the new ones.

Other than switching them over to IMAP, I found the following in the Wiki 
documentation:

#POP3 UIDL format to use. You can use following variables:
  
  # %v - Mailbox UIDVALIDITY
  # %u - Mail UID
  # %m - MD5 sum of the mailbox headers in hex (mbox only)
  # %f - filename (maildir only)
  
  #If you want UIDL compatibility with other POP3 servers, use:
  # UW's ipop3d         : %08Xv%08Xu
  # Courier version 0   : %f
  # Courier version 1   : %u
  # Courier version 2   : %v-%u
  # Cyrus (<= 2.1.3)    : %u
  # Cyrus (>= 2.1.4)    : %v.%u
  
  #Note that Outlook 2003 seems to have problems with %v.%u format which is
  #Dovecot's default, so if you're building a new server it would be a
good
  #idea to change this. %08Xu%08Xv should be pretty fail-safe.
  pop3_uidl_format = %v.%u

So my question is, what happens if I just change pop3_uidl_format to 
%08Xu%08Xv and restart the server? Will it just change things over to the way 
I want them, or will it blow up all the existing mail already being stored 
there?

Inquiring minds want to know. Thanks for any help you can provide.

-- 
Jeff Simmons                                   jsimmons at goblin.punk.net
     Simmons Consulting - Network Engineering, Administration, Security

                "It was on fire when I got here."

A POP3 client will download messages with a different UIDL to any it has 
already downloaded, so you probably want to make the UIDL be generated 
the same way as your previous POP3 server (you don't say which?), unless 
  it's too late and everybody has already connected with to Dovecot with 
different UIDLs and downloaded everything again!

Having said that, the clients should only be downloading the left 
messages once, when you switched to Dovecot.

I'm not sure what the Outlook 2003 problem mentioned is; it may be it 
will always download a message with a %v.%u UIDL. In this case yes, you 
should change it as suggested, but the clients will then download all 
the messages one (hopefully) last time.

Best Wishes,
Chris

Jeff Simmons wrote:
> I recently set up an OpenBSD - Dovecot mail server for a client. Naturally 
> (according to Murphy's Law) they want to use Outlook 2003, pop3s, and
leave
> messages on the server. And just as naturally, the UIDLs don't seem to
be
> working, and when they download mail, they get EVERY email stored on the 
> server, not just the new ones.
> 
> Other than switching them over to IMAP, I found the following in the Wiki 
> documentation:
> 
> #POP3 UIDL format to use. You can use following variables:
>   
>   # %v - Mailbox UIDVALIDITY
>   # %u - Mail UID
>   # %m - MD5 sum of the mailbox headers in hex (mbox only)
>   # %f - filename (maildir only)
>   
>   #If you want UIDL compatibility with other POP3 servers, use:
>   # UW's ipop3d         : %08Xv%08Xu
>   # Courier version 0   : %f
>   # Courier version 1   : %u
>   # Courier version 2   : %v-%u
>   # Cyrus (<= 2.1.3)    : %u
>   # Cyrus (>= 2.1.4)    : %v.%u
>   
>   #Note that Outlook 2003 seems to have problems with %v.%u format which is
>   #Dovecot's default, so if you're building a new server it would
be a good
>   #idea to change this. %08Xu%08Xv should be pretty fail-safe.
>   pop3_uidl_format = %v.%u
> 
> So my question is, what happens if I just change pop3_uidl_format to 
> %08Xu%08Xv and restart the server? Will it just change things over to the
way
> I want them, or will it blow up all the existing mail already being stored 
> there?
> 
> Inquiring minds want to know. Thanks for any help you can provide.
> 

-- 
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Christopher Wakelin,                           c.d.wakelin at reading.ac.uk
IT Services Centre, The University of Reading,  Tel: +44 (0)118 378 8439
Whiteknights, Reading, RG6 2AF, UK              Fax: +44 (0)118 975 3094