Re-indexing Incomplete or Missing Search Results in Apple Mail on macOS and iOS

In some cases, the search function may not provide full or accurate results on macOS and iOS devices. The following is a set of quick fixes to troubleshoot this situation on various device platforms:

macOS / Mail:

Rebuild Mailbox

1. Select the Mailbox/Inbox in question via the Mailbox List / Left Sidebar
2. Go to (Menu Bar) Mailbox > Rebuild
   *Note this can take a long time as it is redownloading your message history.

 
Reindex Spotlight

1. Go to System Settings (Preferences)
2. Click Siri & Spotlight
3. On Spotlight > Search Results toggle “Mail and Messages” Off.
4. Reboot your computer then toggle it back on.

 
Remove and Re-Add Exchange Account

1. Go to System Settings > Internet Accounts
2. Select and Delete your [NU Account]
3. Click "Add Account" and sign back in to Exchange Microsoft 365

iOS / Mail

Search Range Limit

1. Check Settings > Mail > [NU Account] to ensure “Mail Days to Sync” is set to the desired value. 
2. It defaults to “1 Month”, and can alternately be set to “No Limit.”

Re-index Search / Reset Account

iOS does not provide a way to directly rebuild the database, thus removing and re-adding the exchange/mail account is required.

1. Open Settings > Mail > Accounts
2. Select appropriate [NU Account] > Tap “Delete Account”
3. On previous/Mail page, Tap Add Account > Microsoft Exchange
4. Follow the prompts to log in to Microsoft 365 via SSO.