Blocked Sender

Apple support's article:

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

says:

"When you block a phone number or contact, they can still leave a voicemail, but you won't get a notification.

Messages that are sent or received won't be delivered.

Also, the contact won't get a notification that the call or message was blocked.

When you block an email address from Mail, it goes to the trash folder.

Email blocking works across all your Apple devices".

Block calls and messages from certain people – Apple Support

says

"The person you block won’t receive notification that they have been blocked

and you can still call, message or email a blocked contact without unblocking them.

However, if you were sharing your location with them,

they will receive a notification that you have stopped sharing your location after you block them.

Blocking a contact in Phone, FaceTime, Messages or Mail blocks them across all four apps".

Q - " Does the Sender who has been Blocked, come to know that they are blocked? "

A - No

Q - " Or do they assume that the email sent is received by us, but in reality they are blocked at our end? "

A - Not possible Mind Read the senders thought. But, reasonable to conclude that if the Sender continues to send e-mails after you have Blocked them - they still think you are receiving the e-mail.

Most Spammers are using an Automated Workflow so in reality - no actual Human is actually connected.