Electronic Mail Standards: SMTP and X.400

by Lyne Edmonds
Sharda Tarachandra

Network Notes #30
ISSN 1201-4338
Information Technology Services
National Library of Canada

May 31, 1996

1. What are SMTP and X.400?

SMTP (Simple Mail Transfer Protocol) and X.400 are protocols for transmitting electronic mail. They allow disparate e-mail systems running on various operating systems to exchange messages. SMTP is the de facto Internet messaging protocol; it is widely used and strongly supported by software vendors. X.400 is an ISO (International Standards Organization) standard and is officially supported by the federal government. The National Library of Canada supports both SMTP and X.400, so both can be used to send e-mail from the National Library to other organizations.

If the recipient of e-mail can use either X.400 or SMTP, it is preferable to use X.400 when sending e- mail in French or when including attachments. Similarly, people outside the National Library should use X.400, when possible, to send e-mail in French or include attachments. Otherwise, SMTP is the preferred protocol.

SMTP

Simple Mail Transfer Protocol (SMTP) is the Transmission Control Protocol and Internet Protocol (TCP/IP) that governs electronic messaging. TCP/IP has become the de facto Internet messaging protocol. SMTP and X.400 are, in fact, competitors; however, there are good reasons to use either.

Reasons to use SMTP:

• Easy Addressing: SMTP addresses are simpler to remember and use than X.400 addresses.
• Internet Communication: When communicating with anyone outside the Canadian federal government via the Internet, SMTP is the standard most often used and supported.

Disadvantages of SMTP:

• French Diacritics: SMTP does not support French-language diacritics.
• Attachments: Depending on the electronic mail software used, SMTP does not always cope well with sending attachments.

SMTP typically uses Uuencode software to convert binary files (e.g., Microsoft Word or PowerPoint files) into ASCII format so that they can be transmitted via the Internet. For example, MS Mail supports the necessary decoding program (Uuencode) so that attachments sent over the Internet via SMTP can be received. Nonetheless, uuencoding is problematic because there is no guarantee that the external addressee will have access to a uudecoding program to decode the ASCII text. ¹

X.400

The Government of Canada has adopted and is promoting the X.400 standard to encourage communication between federal institutions. Most of the major government departments are establishing or have already established X.400 capabilities.

Technically, X.400 is considered to be more secure and stable than SMTP. Yet this standard has only recently been adopted by the federal government. Therefore, not all departments can be reached via X.400.

Reasons to use X.400:

• French Diacritics: X.400 supports French-language diacritics while SMTP does not.
• Attachments: X.400 is able to send attachments while SMTP needs additional support to do so. Nonetheless, care must be taken with X.400 attachments because original file names are not retained in the transfer. ²

When sending an X.400 message with an attachment, it is advisable to include the original name of the attachment in the text of the message. When an X.400 email message with an attachment is received, it is best to rename the file while still in an electronic mail software such as Microsoft Mail (using the file name given in the text of the message or creating a new file name).

To read the attached document, use a word processor such as Microsoft Word, or in the case of other types of attachments (e.g., graphics or audio files), use an appropriate software package.

Disadvantages of X.400:

• Expensive to Use: Every X.400 message costs the federal government money to transmit.
• Limited Accessibility: X.400 is not widely available to electronic mail users; currently, not all Canadian federal departments have access to X.400 mail messaging.

More organizations have access to MIME (Multipurpose Internet Mail Extensions) than to X.400. MIME is quickly becoming the Internet standard for transmitting extended ASCII characters and mixed media files. However, some organizations are not yet using MIME-compatible electronic mail software.

2. Electronic Mail Addressing

SMTP Addresses

An SMTP address often has two formats -- a real mailbox address and an alias for that address. An alias address points to the real mailbox address, and is easier for people to remember or guess. For most Internet and e-mail activities, the alias should be used (if one exists). All National Library e-mail addresses have aliases consisting of the first and last name of the employee, followed by the National Library domain name (see the example below).

Alias addresses at the NLC use the following format:

Note: SMTP addresses do not permit diacritics and only 32 characters are allowed for name lengths. Addresses are not case sensitive.

Unusual names

Network staff typically consult with staff members to decide how to format hyphenated names (e.g., Anne-Marie Smith), multi-part last names (e.g.,. Suzanne Leblanc-Taylor, Robert De Vito), and names which are shared by two or more people.

X.400 Addresses

X.400 addresses use the following format:

/C=CA/ADMD=GOVMT.CANADA/PRMD=GC+NLC.BNC/G=GivenName/S=Surname

Note: Diacritics are allowed in X.400 addresses and there are no character limits for name lengths. Addresses are not case-sensitive.

2. Within X.400 messages, each attachment is considered to be a separate "body part". For example, when an X.400 message is received with an attachment, Microsoft Mail renames the file with the format BDYnnnnn.xxx. The nnnnn is a number within the message that uniquely identifies the attachment (or body part), and the xxx is the file extension (e.g., BDY1.BIN).