Why is blocking (or quarantining) of emails not an option for POP or IMAP?
POP and IMAP work differently than SMTP. When POP and IMAP are used, the client requests the mail when the user clicks on the email. At that point the message is downloaded from the server and scanned. Even if the application determines the message should not be passed it still must be delivered to the client because the client is waiting and will not be able to read mail unless something is delivered. As a result, only MARK is an option.
POP and IMAP work differently than SMTP. When POP and IMAP are used, the client requests the mail when the user clicks on the email. At that point the message is downloaded from the server and scanned. Even if the application determines the message is spam, it still must be delivered to the client because the client is waiting and will not be able to read mail unless something is delivered. As a result, only MARK is an option.
