This is a great question, since we recently migrated to Office 365 from an on-prem Exchange server.
For us, what caused us to question this is the 49.5 GB of mailbox space -- and the desire to get rid of offline archives. I mean, really, if you don't need to archive, do you really want a cached mailbox that's nearly 50 GB in size? Heck no!
Not to mention whatever you archive is outside the control of IT. If a user loses it, and it hasn't been backed up, it's GONE.
For us, we also wanted the flexibility to be able to have all the laptop users access some cached data so they can easily work while on a plane or otherwise offline.
Our answer applies to Outlook 2013 users:
When setting up the user account in Outlook 2013, you get to choose how much data you want to cache based on a timeline. In the Server Settings =>> Offline Settings select "Use Cached Exchange Mode" and pick how many months (up to six in our case) that you want to cache locally. For us, the magic number was two months.
One extra benefit with Outlook 2013: the cached file is said to be 40% smaller than the cached files created in earlier versions. Now I can have a 50 GB mailbox, avoid the pain of missing archive files -- and still offer the convenience for travelling workers to be able to work offline if they want to. I say that's a good deal!
BTW, if they're not showing the image in this post, try going to
You need to start from scratch on Office 365 and perform a cutover migration following the detailed step-by-step instructions here.
You will need to obtain a valid public SSL certificate and ensure that autodiscover and outlook anywhere (RPC over https) are correctly set up and working. You can test this at http://exrca.com.
If you're unable to make this work (with the free support from MS), then you'll need to hire a consultant to do it for you / show you what to do.
As specified in the instructions, you have to configure DirSync AFTER you have done the mailbox migration.
The reason you have had problems is because you didn't read / follow the instructions provided by MS for a cutover migration:
If you’ve activated and installed the Azure Active Directory Sync
tool, you can’t run a cutover migration. If you’ve already installed
the directory synchronization tool, but haven’t run the tool yet, you
can deactivate directory synchronization in your Office 365 tenant and
then run a cutover migration.
The email migration service uses RPC over HTTP, or Outlook Anywhere,
to connect to your on-premises Exchange server... ...Your Outlook
Anywhere configuration must be configured with a certificate issued by
a trusted certification authority (CA). It can't be configured with a
self-signed certificate.
Best Answer
This was resolved by manually setting the quotas using Exchange Online PowerShell command
Set-Mailbox <UPN> -ProhibitSendReceiveQuota 100GB -ProhibitSendQuota 100GB -IssueWarningQuota 98GB
.On a related note, user mailboxes affected and unaffected by this problem both had
UseDatabaseQuotaDefaults: False
so that seems to be normal.