Emails on iPad suddenly going into Junk or Trash

Changing your mail account passwords will not prevent you from receiving unsolicited/junk/spam email.

For other spam or unwanted email messages that your receive through your email provider (e.g., yourname@yahoo.com), you will need to look for any spam-handling measures that are offered by your email provider.

if Mail is being incorrectly routed to your Junk folder, simply move the email message to your inbox. In this way your Mail App can learn that messages incorrectly categorised as Junk should instead be delivered to your inbox.

Sadly, if your email address is being used as a target for spam, there is little that you can do to stop it; anyone that has your email address can send email to to. Instead you have to “manage” it…

First, be wary of any “unsubscribe” links that may be embedded in the email messages. For the most part, unless the unsolicited email is from a reputable advertiser, the unsubscribe link will not stop the messages. Instead, clicking the link will simply confirm to the spammer that the email address is monitored by a warm-blooded victim - and more spam and unwanted content is likely to come your way.

For unsolicited email, you can use the native blocking feature of iOS/iPadOS to automatically block/delete unwanted email from a sender - although this will only be effective for spam that arrives from a consistent email address:

Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support

Where the spam email is using “spoofed” email sender addresses, your block-list will be ineffective.

The best advice is to avoid becoming a victim. Be careful where you use your email address to subscribe to services. Perhaps keep a secondary address just for this purpose - or, if you have updated to iOS/iPadOS15.1 or later, consider using Apple’s new Hide My Email facility:

What is Hide My Email? - Apple Support

Set up and use Hide My Email in iCloud+ on all your devices – Apple Support

Again, this new feature cannot stop everything, but is another way to reduce the likelihood of receiving and managing email and messaging spam.