When you notice that your iPhone email inbox is overwhelmed with junk email, it might be time to start blocking it so that you don't have to keep dealing with this problem. How to block emails on your iPhone depends on the type of email account you use and what email client or app you are using on your device. Typically, if you send a junk email to the junk folder, your email server learns to send other messages from the same sender directly to the junk folder in the future so you never see them.
How to Block Emails on iPhone Mail
The iPhone comes with a built-in Mail app. The Mail app has a feature to move unwanted mail to the junk folder. If you are using Apple's iCloud mail account, it routes future emails from the same sender directly to the junk folder where you don't have to look at them. This feature doesn't work as well with other email accounts you have configured to run in the Mail account, because those accounts follow their email service provider's rules. You can move those messages to the junk folder, but the action doesn't block the emails automatically in the future as it does with iCloud. To block iCloud junk email on the iPhone, open a junk message on the Mail app and tap the "Flag" icon. Tap "Move to junk" to move that message to your junk folder.
Block Email on Gmail
Gmail allows you to block email addresses that you no longer want to receive mail from on your iPhone. On a computer, you access your Gmail account and then open a message whose sender you want to block. Click the "More" option in the top right side of the email and click "Block [Sender Name]" to block all future emails from this sender from being sent to your Gmail account on your computer or your iPhone.
You can also block junk email directly on your iPhone's Gmail app. Launch the Gmail app and then tap to open an unwanted email. Tap the "More" button on the top right of the screen and select "Report Spam." Gmail will move future emails from this sender to your Spam folder.
Block Email on Outlook
Outlook allows its @outlook.com email address users to block certain email senders from showing up on the iPhone. At the Outlook website at outlook.com, log in to your email account and then click the "Settings" button. Click "Options," then "Mail" and then click "Junk email." Click "Blocked senders" and type in the email address that you want to block. Click the "+" button and then click "Save" to begin blocking any email from that sender.
You can mark junk email on your iPhone's Outlook app. Open the app and locate the email that you want to be considered as junk email. Tap the "Junk" button in the top bar to report the message as junk. Outlook learns from this and should start sending similar emails to your junk folder automatically. If messages still get through, then you should block the sender from a computer.
Block Junk Email on Yahoo
Yahoo's iPhone app lets you mark emails as spam so that they don't show up on your iPhone in the future. Open the app and go to the email that you want to block. Tap the "..." button in the top right corner and select "Mark as spam." The email moves to your Spam folder, and future emails from this sender are automatically flagged as spam and removed from your email inbox.