Lawful Interception (LI); Service specific details for E-mail services

This document shall contain a stage 1 description of the interception information in relation to the process of sending and receiving e-mail. The document gives a stage 2 description of when IRI and CC shall be sent, and what information it shall contain.  The study shall include but not be restricted to SMTP and POP3.  The definition of handover (i.e. transport) of HI2 and HI3 is outside the scope of this document. Refer to DES/SEC 003020.

Zakonito prestrezanje (LI) – Storitveno-specifične podrobnosti za storitve elektronske pošte

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TS ETSI/TS 102 233 V1.2.1:2005
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SIST-TS ETSI/TS 102 233 V1.2.1:2005
Lawful Interception (LI); Service specific details for E-mail services
Ta slovenski standard je istoveten z: TS 102 233 Version 1.2.1
33.020 Telekomunikacije na splošno Telecommunications in
SIST-TS ETSI/TS 102 233 V1.2.1:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS ETSI/TS 102 233 V1.2.1:2005

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SIST-TS ETSI/TS 102 233 V1.2.1:2005

ETSI TS 102 233 V1.2.1 (2004-05)
Technical Specification

Lawful Interception (LI);
Service specific details for E-mail services

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 2 ETSI TS 102 233 V1.2.1 (2004-05)

email, handover, interface, IP, lawful interception,
security, traffic
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© European Telecommunications Standards Institute 2004.
All rights reserved.

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 3 ETSI TS 102 233 V1.2.1 (2004-05)
Intellectual Property Rights.5
Introduction .5
1 Scope.6
2 References.6
3 Definitions and abbreviations.7
3.1 Definitions.7
3.2 Abbreviations.7
4 General.8
4.1 E-mail services.8
5 System model.8
5.1 Reference network topology.8
5.2 Reference scenarios.9
5.2.1 E-mail send failure.9
5.2.2 E-mail send success .10
5.2.3 E-mail download detail.11
5.2.4 E-mail send detail .12
6 E-mail events.13
6.1 Introduction.13
6.2 E-mail send event .13
6.2.1 Introduction.13
6.2.2 E-mail Send captured content .14
6.2.3 E-mail send IRI.14
6.3 E-mail receive event.14
6.3.1 Introduction.14
6.3.2 E-mail receive captured content.15
6.3.3 E-mail receive IRI.15
6.4 E-mail download event.15
6.4.1 Introduction.15
6.4.2 E-mail download captured content .16
6.4.3 E-mail download IRI .16
7 E-mail attributes.16
7.1 E-mail protocol ID.16
7.2 E-mail address.16
7.3 E-mail recipient list .17
7.4 E-mail sender.17
7.5 Total recipient count.17
7.6 Message ID.17
7.7 Status.17
7.8 Server and client port .17
7.9 Server and client octets sent .17
Annex A (normative): SMTP .18
A.1 SMTP introduction.18
A.2 SMTP HI2 events .18
A.2.1 E-mail login event .18
A.2.2 E-mail send event .18
A.2.3 E-mail receive event.18
A.3 SMTP HI2 attributes .19

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 4 ETSI TS 102 233 V1.2.1 (2004-05)
A.4 SMTP HI2 event-record mapping .19
Annex B (normative): POP3 .20
B.1 POP3 introduction.20
B.2 POP3 HI2 events .20
B.2.1 E-mail login event .20
B.2.2 E-mail download event.20
B.3 POP3 HI2 attributes .21
B.4 POP3 HI2 event-record mapping .21
Annex C (normative): IMAP4.22
C.1 IMAP4 introduction.22
Annex D (normative): E-mail ASN.1.23
Annex E (informative): E-mail LI requirements.25
E.1 HI2 requirements.25
E.2 HI3 requirements.26
E.3 General requirements.27
E.4 Requirements mapping.27
Annex F (informative): SMTP characteristics .28
F.1 SMTP service characteristics .28
F.2 SMTP protocol characteristics .28
Annex G (informative): POP3 characteristics.29
G.1 POP3 service characteristics .29
G.2 POP3 protocol characteristics .29
Annex H (informative): Discussion of webmail interception.30
H.1 Webmail network topology.30
H.2 Webmail protocols.30
H.3 Webmail interception.31
Annex I (informative): Discussion for Driving HI2 of HI3.32
I.1 Introduction.32
I.2 Discussion.32
I.2.1 Introduction.32
I.2.2 IP packets.33
I.2.3 TCP packets.33
I.2.4 SMTP packets.33
I.2.5 E-mail messages.33
I.3 Conclusion.34
Annex J (informative): Change Request History.35
History .36


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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 5 ETSI TS 102 233 V1.2.1 (2004-05)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
This Technical Specification (TS) has been produced by ETSI Technical Committee Lawful Interception (LI).
The present document describes what information is required for the handover of intercepted IP-based E-mail traffic
from a Communications Service Provider to an LEMF. The present document covers a stage 2 description of the data,
but does not specify any functionality within the scope of TS 102 232 [3].
The ITU-T Recommendation I.130 [6] method for characterizing a service will be used as a general framework for the
present document. The modified concept of a "stage 1" will be called the "attributes" of the interface. The attributes of
the interface are the sum total of all the constituent attributes that an interface may need to communicate. The modified
concept of a "stage 2" will be called the "events" of the interface. The events of the interface define the rules of the
relationships between the attributes that are required to arrange the disjoint attributes into meaningful information for an
E-mail service interaction.
The present document is intended to be general enough to be used in a variety of E-mail services. It should be
recognized that a side effect of this approach is some IRI fields identified may be difficult to extract or non-existent
depending on the E-mail service being intercepted. In such cases it may be completely reasonable that the delivered IRI
contain empty fields or fields with the value 0.

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 6 ETSI TS 102 233 V1.2.1 (2004-05)
1 Scope
The present document contains a stage 1 like description of the interception information in relation to the process of
sending and receiving E-mail. The present document also contains a stage 2 like description of when Intercept Related
Information (IRI) and Content of Communication (CC) shall be sent, and what information it shall contain.
It is recognized that "Instant Messenger" and "Chat" applications are another way of exchanging electronic text
messages. While the present document may be applicable to such applications it is in no way a goal of the present
document to address these methods of electronic text messaging.
The definition of handover transport and encoding of HI2 and HI3 is outside the scope of the present document. Refer
to TS 102 232 [3].
The present document is designed to be used where appropriate in conjunction with other deliverables that define the
service specific IRI data formats. The present document aligns with TS 133 108 [5], ES 201 671 [4], TS 101 331 [1]
and TR 101 944 [2].
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
• References are either specific (identified by date of publication and/or edition number or version number) or
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
[1] ETSI TS 101 331: "Telecommunications security; Lawful Interception (LI); Requirements of law
enforcement agencies".
[2] ETSI TR 101 944: "Telecommunications security; Lawful Interception (LI); Issues on IP
[3] ETSI TS 102 232: "Telecommunications security; Lawful Interception (LI); Handover
specification for IP delivery".
[4] ETSI ES 201 671: "Telecommunications security; Lawful Interception (LI); Handover interface
for the lawful interception of telecommunications traffic".
[5] ETSI TS 133 108: "Universal Mobile Telecommunications System (UMTS); 3G security;
Handover interface for Lawful Interception (LI) (3GPP TS 33.108 version 5.5.0 Release 5)".
[6] ITU-T Recommendation I.130: "Method for the characterization of telecommunication services
Supported by an ISDN and network capabilities of an ISDN".
[7] IETF RFC 0822: "Standard for the format of ARPA Internet text messages".
[8] IETF RFC 1939: "Post Office Protocol - Version 3".
[9] IETF RFC 2821: "Simple Mail Transfer Protocol".
[10] IETF RFC 3501: "Internet Message Access Protocol - Version 4 rev1".
[11] ITU-T Recommendation X.680/ISO/IEC 8824-1: "Information technology - Abstract Syntax
Notation One (ASN.1): Specification of basic notation".

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 7 ETSI TS 102 233 V1.2.1 (2004-05)
[12] ISO 3166-1: "Codes for the representation of names of countries and their subdivisions - Part 1:
Country codes".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
E-mail Address: ARPANET E-mail address
NOTE: As described in RFC 0822 [7], clause 6.
IMAP4: protocol used to manipulate mailbox parameters on a server
NOTE: Described in RFC 3501 [10].
mailbox: destination point of E-mail messages
POP3: widely used protocol for downloading E-mails from a server to a client
NOTE: Described in RFC 1939 [8].
recipient: E-mail address of a destination mailbox for an E-mail being transmitted
NOTE 1: Each E-mail may contain one or more recipients.
NOTE 2: In this definition there is no distinction made between E-mail addresses on a "To:" line and E-mail
addresses on a "Cc:" or "Bcc:" line. They are all "recipients" of the E-mail.
sender: E-mail address of the mailbox that originated an E-mail being transmitted
NOTE: Each E-mail contains only one sender.
SMTP: widely used protocol for transferring E-mails between computers
NOTE: Described in RFC 2821 [9].
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
APOP POP3 authentication message
ASN.1 Abstract Syntax Notation One
CC Content of Communication
CPE Customer Premises Equipment
HI2 Handover Interface port 2 (for Intercept Related Information)
HI3 Handover Interface port 3 (for Content of Communication)
HTTP Hyper Text Transfer Protocol
IMAP4 Internet Message Access Protocol version 4
IP Internet Protocol
IRI Intercept Related Information
ISDN Integrated Services Digital Network
ISP Internet Service Provider
LEA Law Enforcement Agency
LEMF Law Enforcement Monitoring Facility
MF Mediation Function
MTA Mail Transfer Agents
NWO Network Operator
POP3 Post-Office Protocol version 3
PSTN Public Switched Telecommunication Network

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 8 ETSI TS 102 233 V1.2.1 (2004-05)
RETR POP3 Retrieve message
SMTP Simple Mail Transfer Protocol
SP Service Provider
TCP Transmission Control Protocol
4 General
4.1 E-mail services
E-mail services are those services which offer the capability to transmit or receive ARPANET text messages. The
following description is taken from RFC 0822 [7]:
"In this context, messages are viewed as having an envelope and contents. The envelope contains whatever information
is needed to accomplish transmission and delivery. The contents compose the object to be delivered to the recipient".
E-mail service, in general, can be divided into two categories: those services which allow a computer to transfer a
message to another computer; and those services which allow users to manipulate their mailbox by doing such things as
downloading messages from the mailbox and deleting messages from the mailbox. Both of these categories of E-mail
services can be of interest to Law Enforcement Agencies (LEAs) and are therefore within the scope of the present
NOTE: When using IP-packet delivery, control level packets that are associated with the targeted E-mail may be
delivered as content. Control level packets are those packets that are used by the E-mail transfer protocol
to set-up the E-mail communication and to terminate the E-mail communication and are outside of the
traditional RFC 0822 [7] formatted E-mail. This allows for different interception solutions without
burdening the Mediation Function (MF) with the responsibility of "cleaning" up said differences in input.
5 System model
5.1 Reference network topology
The network topology shown in figure 1 is intended to represent the many relationships that may exist between the
entities involved in E-mail communications. Actual scenarios using this diagram are enumerated in clause 5.2. The
following should be considered when viewing figure 1:
• The term "Mail Server" is used to represent a logical entity that relays mail for its mail clients, receives and
(temporarily) stores mail for its mail clients, and allows mail clients access to the aforementioned stored mail
and the ability to delete it from the mail server.
• The term "Mail Client" is used to represent a logical entity that either injects mail into the network or removes
mail from the network or reads mail from the network.
• Mail Client and Mail Server numbers are used to indicate what entities share a client-server relationship, so
Mail Client1 is a client of Mail Server1, etc.
• A Mail Server may communicate with any other Mail Server within figure 1.
NOTE: Web access to mail is commonly used; web mail is addressed in annex H.

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 9 ETSI TS 102 233 V1.2.1 (2004-05)
Mail Mail
Server Server
1 2
Log Log

IP Network IP Network





IP Network IP Network



Mail Mail CPE

Server Server

4 3

Log Log 3b


Figure 1: Reference network topology
5.2 Reference scenarios
5.2.1 E-mail send failure
It may occur that E-mails sent into the Internet do not reach their intended target. The most common reason for this
would seem to be a mistaken E-mail address, but could also be problems contacting the receiving mail server or other
server issues. Note that a failure reply message is not always generated and if a failure reply message is generated, it is
generated by the Mail Server that first experiences problems transferring the mail message.
a) Client3a sends an E-mail to and gives the E-mail to the clients' server, Mail
b) Mail Server3 fills in part of the E-mail envelope and routes the E-mail to Mail Server4.
c) Mail Server4 replies to Mail Server3 that the recipient is unknown.
d) Mail Server3 creates a "reply" message to Mail Client3a stating that the recipient was unknown, and either
pushes that message to the client or stores it in the clients' mailbox for later retrieval.

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 10 ETSI TS 102 233 V1.2.1 (2004-05)
Log Log


IP Network IP Network

Mail Mail

Client2 Client1


IP Network IP Network










Figure 2: E-mail send failure
5.2.2 E-mail send success
This scenario represents what is likely to be the most common case of an E-mail send. While it is unclear how many
E-mails go directly from a clients E-mail server to the destination E-mail server, it is clear that routing of E-mails
through Mail Transfer Agents (MTA) is not uncommon and as such is the scenario represented here. The direct routing
scenario is a subset where the middle mail server is removed. Note also that the client sending the E-mail is not on the
same administrative network as its mail server.
a) Client1 sends an E-mail to and gives the E-mail to the clients' server, Mail
b) Mail Server1 fills in part of the E-mail envelope and forwards the mail to Mail Server4 for forwarding.
c) Mail Server4 attaches its information to the E-mail envelope and forwards the mail to Mail Server3.
d) Mail Server3 either pushes the message to the Mail Client3b or stores it in the clients' mailbox for later

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SIST-TS ETSI/TS 102 233 V1.2.1:2005
 11 ETSI TS 102 233 V1.2.1 (2004-05)
Mail Mail
Server Server
1 2
Log Log
IP Network

IP Network



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