riddlebox:~$ rfc -k ingress
The Result:
2267 Network Ingress Filtering: Defeating Denial of Service Attacks
     which employ IP Source Address Spoofing. P. Ferguson, D. Senie.
     January 1998. (Format: TXT=21032 bytes) (Status: INFORMATIONAL)

riddlebox:~$ rfc -k pop

The Result:
1734 POP3 AUTHentication command. J. Myers. December 1994. (Format:
     TXT=8499 bytes) (Status: PROPOSED STANDARD)
1957 Some Observations on Implementations of the Post Office Protocol
     (POP3). R. Nelson. June 1996. (Format: TXT=2325 bytes) (Updates
     RFC1939) (Status: INFORMATIONAL)
2095 IMAP/POP AUTHorize Extension for Simple Challenge/Response. J.
     Klensin, R. Catoe, P. Krumviede. January 1997. (Format: TXT=10446
     bytes) (Obsoleted by RFC2195) (Status: PROPOSED STANDARD)
2195 IMAP/POP AUTHorize Extension for Simple Challenge/Response. J.
     Klensin, R. Catoe, P. Krumviede. September 1997. (Format: TXT=10468
     bytes) (Obsoletes RFC2095) (Status: PROPOSED STANDARD)
2384 POP URL Scheme. R. Gellens. August 1998. (Format: TXT=13649
     bytes) (Status: PROPOSED STANDARD)
2449 POP3 Extension Mechanism. R. Gellens, C. Newman, L. Lundblade.
     November 1998. (Format: TXT=36017 bytes) (Updates RFC1939) (Status:
     PROPOSED STANDARD)
2595 Using TLS with IMAP, POP3 and ACAP. C. Newman. June 1999.
     (Format: TXT=32440 bytes) (Status: PROPOSED STANDARD)