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The boss of a company for whome I am responsible for their exchange server has a full mailbox. The current mailbox limit is 2Gb (pretty standard).

He's asked if I can bump his mailbox up to something around 10Gb in size. The exchange server is located on the same physical network as he is on 95% of the time.

Is there any "gotchas" I should know about before agreeing to bump his mailbox to 10Gb? What issues may we encounter if he actually fills his account to 10Gb?

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You know that MS has recommended 4gb to be the minimum anyway? And that WAS meant as minimum. – TomTom Jan 7 '13 at 9:21
up vote 10 down vote accepted

As long as you've got the disk space and backup capacity there's not really an issue. Exchange has been able to handle large mailboxes for a long time, and Exchange 2010 does a stellar job.

Outlook would be the only place where I'd have any cause for concern, and then only if the user is using an older version (pre-2007). Newer versions of Outlook aren't going to have problems with such a large mailbox (and older versions really won't, either, unless you're doing caching).

The only performance problems I've seen with Outlook and large mailboxes relate to large numbers of individual items in folders, but that's more of a count-of-items problem and not a size-of-items problem. The user shouldn't keep 20,000+ items in a single folder and expect it to perform well.

You might consider using the personal archives feature in Exchange 2010 if the user needs to keep a lot of old data around, but there's no reason you can't keep it in his mailbox, just as well.

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It's been my experience that Outlook is hampered more by the number of items rather than the size of the mailbox, as Evan stated. The general number I've always come back to (from my own research and from speaking to MS) is to keep 2,000 to 5,000 items or less per mailbox folder. – joeqwerty Jun 1 '11 at 23:37
I'll second @joeqwerty 's estimates. Even on machines with more RAM Outlook starts to choke with large item counts. I have noticed, however, that the more items per operation the more it chokes. Cached mode helps performance, although you do take a hit with the sync during startup. – squillman Jun 2 '11 at 0:35
They don't have a premium license for exchange, so online archives can't be used. But glad to know that he'll be OK. It's Outlook 2010 as well - yippee for clients that have Software Assurance and actually use it. – Mark Henderson Jun 2 '11 at 1:42
I have mailboxes with hundreds of thousands of items. Outlook chokes on number of items per folder so as long as you keep it under 5-7K items per folder theh mailbox can contain alot of items. Outlook 2010 has really raised te bar on the number of items. My personal mailbox has a folder with 11172 items and it has no issues.(outlook 2k10,x86 on win7 x64) – Jim B Jun 2 '11 at 2:22
Yeah, same as JimB, I have a couple of hundred thousand items in my mailbox, but I have all my mail sorted by year and month (going back many years) so never too many messages in any given folder. I also have very very few messages with attachments, I relentlessly strip them out. – Ward Jun 2 '11 at 2:49

I'm going to add another consideration to Evan's answer. Users with large mailboxes lead to large databases. The larger the database, the longer the recovery time in the event of a disaster. That's something the boss should be made aware of. How many hours is it going to take to recover a database with 10GB mailboxes?

You could plan for high availability by keeping copies of the database on multiple servers. DAGs in Exchange 2010 totally rock! If the budget isn't available for that, consider moving into the cloud with hosted Exchange (make high availability somebody else's problem to worry about).

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I hate the term "cloud", I love the term "someone else's problem"... ;) – Mark Henderson Jun 2 '11 at 2:06
Good point about recovery times (backup times too). – joeqwerty Jun 2 '11 at 2:06

If he gets to 10GB, he may start to notice performance issues compared to what he has today, but I have had MANY users with 6-8GB mailboxes with no problems. That said, Exchange 2010 has improved the compression algorithms with Outlook 2010, so they are even more efficient than Exchange 2007, and way better than 2003. The only caveat: Don't do it if you are not running gigabit Ethernet.

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To expand on my comment on Evan's answer, my experience is that mailboxes are never too large because of the messages, it's the attachments that cause them to grow. Limiting message size helps, but like most places, people here are always sending around powerpoint files and documents with pictures and it doesn't take too many 20MB files to add up to a GB. The problem is that email provides useful meta-data to many people: I sent this version of the file to these people on this date.

I haven't been terribly successful, but I'm always working on getting people to save their attachments, and then (or simply) delete them. In a couple of cases, I was able to train someone with a big mailbox to use MessageDetach to extract attached files, but that's about a 1% success rate.

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According to Microsoft, it is not the size that matters, it's the number of items.

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