Marking an email as "Junk" and blocking a sender can result in two different things

CooverCoover35 

I am an independent advisor responding to this inquiry.

I could not recreate your issue in Outlook for the web - business & enterprise environments.  I tested the following behaviors:

• blocked sender read and unread messages 
• report junk vs block sender

And the marked messages were moved to the Deleted folder, and all future messages will go directly to the Junk folder for 30 days as designed. If you have several messages already in your Inbox from this now blocked sender, you can use the Sweep command to move the remaining messages. The top two choices will work for you.

I also encourage you to give Microsoft feedback to either delete or move all existing labeled block sender's emails to the deleted or junk folder. (You will get  my vote. )
 

You are correct. Email marketers get smarter everyday by changing the username@ of the email address. However, you can also block the domainname.com as long as it is not a host provider domain like aol.com, gmail.com, yahoo.com, or outlook.com. 

• Settings icon | View All Settings | Mail | Junk 
• +Add | input the domainname.com

It appears that you know how the Junk Email suppose to behave. I would like to take this opportunity to educate others who may be reading this post. 

Outlook for the Web: Recently, Microsoft separated Junk Emails drop-down menu into two categories:

• Report: Report Phishing and Report Junk
• Block: Block Sender and Never Block Sender

They are located in the top navigation. You may need to select the More options (three dots) to see these choices.

Report Phishing: Suspicious fraudulent mail requesting for personal information; possible virus; protection from hackers
Report Junk:  Unknown Senders (Bot marketers); your email was part of a purchase email database or list

Block Sender:  You once subscribed, joined or provided your email details but no longer interested

Never Block Sender: A trusted sender

If you find this information useful, please mark it as the best answer or like this post which will assist others with the same question.

/Teresa

#traccreations4e