All Inboxes in Mail app showing only five messages
Reset the email account within the Mail App


Go to Settings > Passwords &amp; Accounts > Accounts 


Or Settings > Mail ( or Mail, Contacts, Calendars) > Accounts

Select the mail account that shows the incorrect unread mail notifications


If you have more than one, perform these steps for each account

Toggle OFF “Mail” to disable it. This action does not delete your account





Exit Settings by returning to your Home Screen
Close the Mail app by swiping up your Gesture Bar or by pressing the Home button twice. Locate the Mail app preview and swipe up to close it
Now once again go to Settings > Passwords &amp; Accounts > Accounts


For older iOS, go to Settings >Mail (Mail, Contacts, Calendars) and select the mail account

Toggle ON Mail to enable it.
Check to see if your mail app is now showing the correct unread email counts.