How big can IMAP accounts be and outlook still works OK?

I'm dealing with a friend's laptop that is really slow.  He has several imap accounts for his domains that he has hosted from gmail and set up in outlook 2010.  They seem to be huge.  The PSTs (for imap? Or is that for the local folders under that account?  there's 3 PSTs for different email accounts - 7GB, 2GB and 3GB and 3 more that are about 0.5GB.  For the last half hour, it's been syncing mail

the icon at the bottom right says '
progress 25%
Action loading Outlook Events
Item 785 out of 1143

(i'm thinking that's 785 of 1143 for 1 mail account and there's others it hasn't started yet, that it says it's 25% complete?).

What kinds of limits are there for email and imap?  I am only used to PSTs / POP mail.  You hear about hosted exchange coming with 25GB (max) mailboxes.  Exchange is kinda like IMAP, right?  What's the performance of a laptop w/ outlook and exchange mailbox at 15 - 20 - 25GB?  

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Frosty555Connect With a Mentor Commented:
IMAP and Exchange are very different. They are similar only in the idea that the mail is stored on an outside server as opposed to a local computer. The protocols themselves are totally different.

Unfortunately IMAP is a bit clunky. The main issue is that it needs to download and parse all of the headers in an (almost) synchronous manner.

When Outlook is the bottleneck (e.g. with PST files or Exchange mailboxes), the limitation depends on the version of Outlook. Outlook 2003 is ~4GB or 3000 items. Outlook 2007/2010 is closer to 20GB / 100,000 items before the performance degradation is unbearable. With big mailboxes Outlook is usually unbearably unresponsive until a complete copy of the mailbox is cached locally. This usually means letting Outlook sit overnight as it caches the Exchange mailbox.

However IMAP imposes it's own limits. In general if there are more than about 4000-5000 items in any particular folder it tends to bog down.  Outlook 2007/2010 is much better at telling you about the progress of downloading headers. Outlook 2003 tends to just hang while it is working which can be frustrating for users.

I do find that the main thing that causes IMAP to mess up is when the connection to the IMAP server fails for whatever reason - latency, flaky internet, etc. A good solid internet connection is important to having a good IMAP experience as it doesn't recover from a connection failure well. If you've been sitting at 25% for the last half an hour you probably have experienced a connection failure. Closing and re-opening Outlook will most likely let it continue.

Also, if your internet connection will allow, have Outlook configured to sync headers first, then full items including attachments. Having Outlook cache a complete local copy of the mailbox will reduce the lagging when switching from one message to another.
BeGentleWithMe-INeedHelpAuthor Commented:
Thanks.  I meant that after 1/2 hour, it was only 25% done.  Now, 1/2 hour after I posted that at 17:52:22, actually the send / receive status in bottom of outlook says 64% ... (now 73% after a few minutes of typing this)and the synch? icon in the task bar says 945 of 1143 and 26%?  So I guess it's moving.

with IMAP, the emails are stored on the server, but there is some info (headers?) of each stored on the desktop?  In the PST file?
Frosty555Connect With a Mentor Commented:
Okay, that means it's working, you just have to be patient while it downloads the messages. This probably means your Internet is slow, or your IMAP provider is not giving you very much bandwidth, or those messages have awfully big attachments in them.

In any case, after it syncs all the messages it won't need to do it again, so you should be okay after that.

In IMAP, the client (e.g. Outlook) is supposed to first download the headers and cache them. Then it downloads the full message contents and caches that. The caches are strictly caches and are not intended to be treated as an actual copy of the messages. They will regularly be overwritten with new data from the IMAP server or deleted when the IMAP server says those messages no longer exist.

... But yes, internally the storage used is a .PST file. By default it is in the C:\Users\[username]\AppData\Local\Microsoft\Outlook folder.
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