science

International email

International email is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand International email rather than just read about it. In short: International email arises from the combined provision of internationalized domain names (IDN) and email address internationalization (EAI). The result is email that contains international characters (characters which do not exist in the ASCII character set), encoded as UTF-8, in the email header and in supporting mail transfer protocols.

Key takeaways

International email belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect International email to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of International email from memory before moving on to harder problems.

Reference excerpt

International email arises from the combined provision of internationalized domain names (IDN) and email address internationalization (EAI). The result is email that contains international characters (characters which do not exist in the ASCII character set), encoded as UTF-8, in the email header and in supporting mail transfer protocols. The most significant aspect of this is the allowance of email addresses (also known as email identities) in most of the world's writing systems, at both interface and transport levels.

Email addresses Traditional email addresses are limited to characters from the English alphabet and a few other special characters. The following are valid traditional email addresses:

stellyamburrr985@example.com (English, ASCII) Abc.123@example.com (English, ASCII) user+mailbox/department=shipping@example.com (English, ASCII) !#$%&'*+-/=?^_`.{|}~@example.com (English, ASCII) "Abc@def"@example.com (English, ASCII) "Fred\ Bloggs"@example.com (English, ASCII) "Joe.\\Blow"@example.com (English, ASCII)

A speaker of a language using Cyrillic might wish to use a string like бацка.махно as their identifier, but be forced to use a transliteration such as batska.makno@example.org or even some other identifier instead. The same is true of Chinese, Japanese, and other nationalities that do not use Latin scripts, but also applies to users from non-English-speaking European countries whose desired addresses might contain diacritics (e.g. André or Płużyna). As a result, email users are forced to identify themselves using non-native scripts, which may result in errors due to ambiguity of transliteration (for example, иван.сергеев may become ivan.sergeev, ivan.sergeyev, or something else). Alternatively, developers of email systems must compensate for this by converting identifiers from their native scripts to ASCII scripts and back again at the user interface layer. International email, by contrast, uses Unicode characters encoded as UTF-8—allowing for the encoding the text of addresses in most of the world's writing systems. The following are all valid international email addresses:

用户@例子.广告 (Chinese, Unicode) ಬೆಂಬಲ@ಡೇಟಾಮೇಲ್.ಭಾರತ (Kannada, Unicode) अजय@डाटा.भारत (Hindi, Unicode) квіточка@пошта.укр (Ukrainian, Unicode) χρήστης@παράδειγμα.ελ (Greek, Unicode) Dörte@Sörensen.example.com (German, Unicode) коля@пример.рф (Russian, Unicode) مثال@موقع.عر (Arabic, Unicode)

UTF-8 headers Although the traditional format for email header section allows non-ASCII characters to be included in the value portion of some of the header fields using MIME-encoded words (e.g. in display names or in a Subject header field), MIME-encoding must not be used to encode other information in a header, such as an email address, or header fields like Message-ID or Received. Moreover, the MIME-encoding requires extra processing of the header to convert the data to and from its MIME-encoded word representation, and harms readability of a header section. The 2012 standards RFC 6532 and RFC 6531 allow the inclusion of Unicode characters in a header content using UTF-8 encoding, and their transmission via SMTP—but in practice support is only slowly rolling out.

Interoperability via downgrading Domain internationalization works by downgrading. UTF-8 parts, known as U-Labels, are transformed into A-Labels via an ad-hoc method called IDNA. For example, sörensen.example.com is encoded as xn--srensen-90a.example.com. In 2003, when the need was addressed, that seemed easier than checking that all DNS software could comply with UTF-8 strings, although in theory DNS can transport binary data. This encoding is needed before issuing DNS queries. Since traditional email standards constrain all email header values to ASCII only characters, it is possible that the presence of UTF-8 characters in email headers decreases the stability and reliability of transporting such email. This is because some email servers do not support these characters. Checking compliance with UTF-8 strings must be done software package by software package (see #Adoption below.) There was an experimental method proposed by the IETF, by which email could be somehow downgraded into the legacy all-ASCII format which all standard email servers support. This proposal was deemed too cumbersome; the meaning of the left hand side part of an email address is local to the target server, and so there is no way to check whether xn--something is a valid user name, used in some domain. It was later obsoleted in 2012.

Standards framework The set of Internet RFC documents RFC 6530, RFC 6531, RFC 6532, and RFC 6533, all of them published in February 2012, define mechanisms and protocol extensions needed to fully support internationalized email addresses. These changes include an SMTP extension and extension of email header syntax to accommodate UTF-8 data. The document set also includes discussion of key assumptions and issues in deploying fully internationalized email. Unicode also has recommended Email Security Profiles for Identifiers.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with International email

Start with the simplest possible case. Write down what International email claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to International email before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about International email ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of International email

In research: International email appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses International email in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: International email is common in secondary-school and first-year university syllabi. It links to neighbouring topics Email, so understanding it makes those chapters shorter.
In everyday life: Look for International email outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study International email in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what International email means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain International email out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is International email in simple terms?

Why does International email matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study International email?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on International email.