Action	SMTP	POP/IMAP
Spam	Reject	Yes	No
	Drop	Yes	No
	Accept	Yes	Yes
	Tag	Yes	Yes
	Forward (change recipient)	Yes	No
Virus	Deliver	Yes	No
	Do not Deliver	Yes	No
	Strip & Deliver	Yes	Yes

 

With POP3 and IMAP protocols, as mail client initiates the mail transfer and is already aware about the number of mails to be received, Cyberoam cannot reject any mails.

Due to this limitation of POP3 implementation, Cyberoam cannot reject mails even if they are infected. As an alternative, to inform the user about spam and virus infected mails, Cyberoam has a provision to tag the mail transferred via any of the Mail protocols and lets the user deal with the mail. 

Similar is the case with IMAP implementation, while with SMTP protocol this is not the case hence Cyberoam can reject the mail if required.

By tagging POP3 and IMAP spam mails, user has a flexibility to move the tagged mails to a separate folder or automatically delete indicating in the scanning rule to check for the tagged text in the subject line of the mail.

 

POP3 RFC

As per the RFC 1939, The Post Office Protocol - Version 3 (POP3) is intended to    permit a client/user/workstation to dynamically access a maildrop on a server.  This means that the POP3 is used to allow a workstation to retrieve mail that the server is holding for it.  

In other words, when the POP3 client sends request for the mail transfer, mail is already dropped in the mail server. Mail client simply “pops” or “polls” the mail from mail server.  

Again as per the RFC 1939, POP3 is not intended to provide extensive manipulation operations of mail on the server.