How can I fix email notification issues on my iPhone with iOS 18.2?

You may want to check that Alerts is turned on for each of your email addresses.

To do this:

1. Go to Settings > Notifications > Mail
2. Tap Customise Notifications
3. Select each email account individually
4. Ensure that Alerts and Badges are enabled
5. Choose the correct notification sound
6. Make sure 'All Unread Messages' is selected

If the issue persists, try force restarting your iPhone.

Check this, first.

Or Use and customize the Action button on iPhone - Apple Support (IN)

Then please check the following.

• Check your DND status - Settings > Focus [Do Not Disturb]; Use Focus on your iPhone, iPad, or iPod touch - Apple Support
• Check BedTime Status - Clock App; Use Bedtime to track your sleep on your iPhone - Apple Support
• Check your iPhone Sound Volume; Adjust the volume on your iPhone - Apple Support
• Check Call Audio Routing; Call Audio Routing Bluetooth / Speaker / Automatic
• Check Auto Answer Calls; Turn off Auto Answer Calls
• Check the list of Blocked Numbers --> Block phone numbers, contacts, and emails on your iPhone ...

Notification Preview when Screen is Locked, Notification Alerts, Notification OFF, and much more...

1. To get Notifications when the Screen is locked see the pic below which is self-explanatory
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2. To turn ON notifications selectively for apps, go to Settings > Notifications > Scroll Down to the App and turn ON notifications... Change notification settings on iPhone - Apple Support (IN)
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3. Some apps have their own notification settings over and above the iOS notification settings: An example of Instagram Notification settings is given below
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4. Help for Notification Alerts --> No Notification Alerts - Apple Community