Avoid IMAP/ POP3 clients re-download all mails

alejandroid · Post by **alejandroid** » Fri Sep 06, 2013 3:22 pm

Hello everyone.
We have been testing ZCS Open Source Edition v.8 and our experience has been very good.
Now we are moving to the migration stage from SUN JES (POP3/IMAP/LDAP) to ZCS OSE 8, successfully migrating users / password and mailboxes using imapsync.
However, when IMAP/POP3 clients (about 2000) connect to the new mailbox, all mails (600GB) are downloaded (POP3) or synchronized (IMAP) causing severe network problems, and making our migration unviable.
For POP3 clients we found this workaround: Prevent duplicates messages for POP3 users post migration - Zimbra :: Wiki and it seems to work fine and resolve this issue, but what happens with IMAP? I did some test and the workaround apparently helps but I'm not entirely sure.
We are trying to make migration transparent to users, so that they do not even notice the change in the infrastructure.
what are your opinions or suggestions?

7531prashant · Post by **7531prashant** » Wed Sep 11, 2013 6:45 am

Do you have same configuration setting(server name, port, SSL etc.) on new zimbra server to of existing SUN JES? If not then you need to configure IMAP account again for each user.
Mail client Configuration - Zimbra :: Wiki

alejandroid · Post by **alejandroid** » Wed Sep 11, 2013 11:46 am

[quote user="7531prashant"]Do you have same configuration setting(server name, port, SSL etc.) on new zimbra server to of existing SUN JES? If not then you need to configure IMAP account again for each user.
Mail client Configuration - Zimbra :: Wiki[/QUOTE]
Hello Prashant, thanks for answering. Both Servers have same configuration setting, and user can connect without problems after migration, the problem comes when the email clients (Outlook, Thunderbird) look into the migrated mailbox (using imapsync) and see all messages as new, causing all the messages be re-downloaded (POP3) or re-synchronize (IMAP), causing severe network problems, and making our migration unviable.
I think its relative to preserving IMAP UIDs and POP3 UIDLs, but how I can accomplish this?
Any opinion or suggestion is appreciated

ppearl · Post by **ppearl** » Thu Sep 12, 2013 10:30 am

Unfortunately, there is no way to preserve IMAP UIDs nor POP3 UIDLs with ZCS.
When using the zimbraPrefPop3DownloadSince attribute you referenced, you need to be careful to ensure that the timestamp you set is before or equal to the last time a user POP'd their mail last successfully. Otherwise you run the risk of having the POP client missing messages between the last POP time and the time you set in zimbraPrefPop3DownloadSince.

alejandroid · Post by **alejandroid** » Thu Sep 12, 2013 11:46 am

[quote user="2422ppearl"]Unfortunately, there is no way to preserve IMAP UIDs nor POP3 UIDLs with ZCS.
When using the zimbraPrefPop3DownloadSince attribute you referenced, you need to be careful to ensure that the timestamp you set is before or equal to the last time a user POP'd their mail last successfully. Otherwise you run the risk of having the POP client missing messages between the last POP time and the time you set in zimbraPrefPop3DownloadSince.[/QUOTE]
Hello ppearl, ok now is clear. As a workaround we are considering no migrate mailboxes and allow both servers - SUN JES with old messages and ZCS with new messages - be consulted by users. Is there another way you could recommend? We are talking about 2500 users and 600GB mailboxes.

ppearl · Post by **ppearl** » Thu Sep 12, 2013 4:06 pm

In the end, 600GB isn't *that* big. Every situation is different and you'll need to make a judgement call based on what is right for your business and what your infrastructure can support.
Earlier you stated, "We are trying to make migration transparent to users, so that they do not even notice the change in the infrastructure."
In many (most?) cases, you bite the bullet and migrate the data. If there are bandwidth/cpu/disk constraints, you might consider an approach where you only migrate X accounts in a defined time period to reduce the load on the limiting resource(s). By staggering the migration over a period of time you can hopefully have better control over what will happen and how it impacts your customers.
If you don't migrate the data, you're guaranteed to impact every user, no? Potential issues include:

- Each user needs to setup a new account on their POP/IMAP clients if they use those.

- Usage for the end user likely becomes inconvenient as they possibly have to go to two places to look for data.

- The capabilities of the two platforms may differ enough to be difficult to support.

- Administratively and support staff impacts likely include:

- need to maintain and backup two platforms

- need to ask users which platform they are having problems with (or where you need to restore from?)

- etc.
Having IMAP clients re-sync is typically not more than an annoyance in the long run.

Having POP clients re-download is pretty annoying (try to get users off POP?), so setting zimbraPrefPop3DownloadSince to some reasonable value for each account helps mitigate that somewhat.

Web users will likely appreciate having their email in one place on the new system, but they will need to adjust to a new UI.

alejandroid · Post by **alejandroid** » Fri Sep 13, 2013 5:14 pm

Hello ppearl, thanks a lot for your time & attention.
Your answer help me to see things from another perspective: Since we have many POP3 users and We have a workaround for this, I think with a good strategy We can manage IMAP clients re-sync.
My experience with zimbra has been very good and with this excellent collaboration I'm sure it will be a success, I'll let you know the results.

wellington1993 · Post by **wellington1993** » Mon Mar 14, 2016 1:30 pm

Please try: https://wiki.zimbra.com/wiki/Download_t ... cific_date