Reduce Mailbox Size

If your mailbox gets too large, Outlook slows down — and eventually you can't send mail at all. The fixes below shrink the mailbox without losing access to your mail. Start with the quick cleanup; the shared-mailbox settings are where the big wins usually are.

Option A — keep less shared mail offline

File → Account Settings → Account Settings → select the shared mailbox → Change → drag the Mail to keep offline slider to a shorter period. You can set this per mailbox.

Option B — stop downloading shared folders (most effective)

File → Account Settings → Account Settings → select your own account → Change → More Settings → Advanced tab → untick Download shared folders → OK, Next, Finish. Shared mailboxes then stay online-only: slightly more network use, dramatically smaller data file.

Option C — add the shared mailbox as its own account

File → Account Settings → Account Settings → New, enter the shared mailbox's address, and follow the prompts. Each mailbox then gets its own data file instead of inflating yours.

Leave the advanced fixes to IT

There are also fixes involving the Windows Registry (raising the data-file size limit) and the Exchange admin center (online archiving for shared mailboxes). Don't attempt these yourself — if the options above haven't solved it, submit a ticket and IT will take it from there.

Submit an Argus IT ticket. Tell us your mailbox size if you know it (File → Tools → Mailbox Cleanup shows it), which shared mailboxes you have attached, and which of the options above you've already tried.