The SMTP kioslave currently conforms to the following SMTP-related RFCs:

Base Spec:
2821 Simple Mail Transfer Protocol. J. Klensin, Ed.. April 2001.
     (Format: TXT=192504 bytes) (Obsoletes RFC0821, RFC0974, RFC1869)
     (Status: PROPOSED STANDARD)

Encryption/Auth:
3207 SMTP Service Extension for Secure SMTP over Transport Layer
     Security. P. Hoffman. February 2002. (Format: TXT=18679 bytes)
     (Obsoletes RFC2487) (Status: PROPOSED STANDARD)

2554 SMTP Service Extension for Authentication. J. Myers. March 1999.
     (Format: TXT=20534 bytes) (Status: PROPOSED STANDARD)
(with all SASL mechanisms supported by KDESasl)

General:
1652 SMTP Service Extension for 8bit-MIMEtransport. J. Klensin, N.
     Freed, M. Rose, E. Stefferud, D. Crocker. July 1994. (Format:
     TXT=11842 bytes) (Obsoletes RFC1426) (Status: DRAFT STANDARD)

1870 SMTP Service Extension for Message Size Declaration. J. Klensin,
     N. Freed, K. Moore. November 1995. (Format: TXT=18226 bytes)
     (Obsoletes RFC1653) (Also STD0010) (Status: STANDARD)

2920 SMTP Service Extension for Command Pipelining. N. Freed.
     September 2000. (Format: TXT=17065 bytes) (Obsoletes RFC2197) (Also
     STD0060) (Status: STANDARD)

Known shortcomings:
- Doesn't enforce the CRLF lineending convention on user-supplied data.
- Due to the lack of a Mulit_Put_ in the KIO infrastructure, pipelining
  across messages isn't supported.