Technical features

This page of information is certainly the least accessible of this web site. It is necessary to have a knowledge of the format of the messages transmitted by electronic mail (in particular encoding MIME) to follow all the details.

General

At the beginning, Internet protocols were developed for the United States of America, before being used in other countries.
This internationalization required to take into account alphabets richer than the American alphabet.
Moreover, after the basic texts, the protocols of electronic mail integrated the possibility of sending texts with page-setting and file of any nature.
Unfortunately, for each encountered problem, several distinct technical solutions were adopted, without most of the time, such a diversity had of practical interest.
In addition, the complexity of the standards makes that they are not exactly respected by the mailers, due to difficulties of application, or due to very aproximative implementation.
In practice, the majority of the mailers use a limited subset of the possible formats of messages.

Two choices are thus possible:

either to try to support as well as possible all the messages with the risk to carry out a very complex application
or to limit itself to the most current cases (which can nevertheless include 99 % of the messages).

It is the second approach which was adopted for Libremail.
However, version after version, Libremail supports more and more particular cases, without to having become much more complex than at the begining.

Processing of the received mails according to their structure

If the received mail is limited to a zone of text of the text/plain type, Libremail will display this text.

In the case of messages multipart/alternative (at first some then the equivalent in HTML), Libremail will display the text section of the mail.

If the mail is in pure HTML (text/html), Libremail does not make conversion to display this kind of message in a way easy to read.
However, the tool suphtm is able to detect and remove before downloading the messages in pure HTML.

If a mail is of multipart/report type, Libremail will display the various zones of text which it contains the ones following the others.
There is no search for files joined in the mails of the multipart/report type.

In the case of a mail of the multipart/mixed type, Libremail will display the text contained in the first section. According to case's, it will be:

the text contained in a section of the text/plain type,
the text/plain under section of a multipart/alternative section,
the text not converted of the text/html section if there is no text/plain section

Structure of the messages sent

For the sending of mails, Libremail is only limited to two structures of message:

mail only made up of one section text of the type text/plain
mail of the multipart/mixed type composed of a section text/plain followed one or more attached files.

Encoding of the characters

As specified higher, protocols Internet initially were American before being internationalized. However, American population has 2 characteristics which distinguish them from the majority of the people of planet:

they have a disproportionate stock of massive destruction weapons,
their language does not include any accent.

For the electronic mail, it is the 2nd point which is most important, in particular because in the beginning, Internet protocols were planned for a transmission of the characters on 7 bits.
Under these conditions the characters having the 8th significant bit (set to 1) had to be encoded.
Remainder, even today where the transmission of the characters on 8 bits spread, the standard of transmission provides that the characters of the heading of the messages having the 8th positioned significant bit will be always encoded.
Two formats of encoding exist: the format "quoted printable" and the format base64.

For the display of the fields of the heading of the messages, Libremail supports since the beginning the encoding quoted printable (quasi universal) and since version 1.0.4 the encoding base64 (much rarer and without practical interest with a European alphabet, except may be to prevent a readable display with old mailers, and to complicate the filtering of the mails directly by the server of transport starting from the Subject: field).

For the display of the contents received messages, libremail accepts since the beginning the texts forwarded directly on 7 or 8 bits (without encoding visible during the reception), and the messages encoded with the format quoted printable.
The base64 encoded messages are now converted (since version 1.1.0), but with a jumps of line processing more rudimentary than for the other formats. In all way, the use of this encoding for the texts of the mails is very rare, and completely unjustified with a European alphabet.

For the recovery of the attached files, the quoted printable and base64 encodings are both converted since the beginning, (what is least things).

For the sending of mails, Libremail carries out an encoding quoted printable automatically fields of the heading which contain special characters, whereas the body of the messages is transmitted under 8-bits and thus, without encoding.

To send attached files, according to the contents of these files, Libremail chooses between the encoding quoted printable and the encoding base64, that which is the least cumbersome.

These technical choices are appropriate perfectly in the developed countries (for example France), but are not can be adapted to other areas of the world like Africa (to be checked).
If it proved that in these countries, the accentuated characters are correctly transmitted in the fields of heading (in particular in the subject of the mail), and in the enclose files, but not in the text of the message, it would be necessary to create and use a modified version of "envmail" so that these messages are transmitted with the encoding quoted printable.

Recognized character sets

A the origin, Libremail was conceived to work with the default character set ISO-8859-15 or ISO-8859-1 when the symbol € (euro) is not necessary.
It can thus display without conversion the mails resulting from a PC working as well under Windows (up to version 98), as under some distributions of GNU/Linux and other UNIX.
A subset of the characters (nondisplayable in this state) included in the interval 80h at 9Fh (used in particular on Mac) is converted in its equivalent in the ISO-8859-15 set.
Libremail also detects UTF-8 encoding and converts the corresponding characters when they are equivalent to a character present in the A0h interval at FFh of ISO-8859-15 set.
Those which correspond to a character of the interval 80h at 9Fh in this ISO set are not converted. On the one hand one would lead to nondisplayable characters, other share their encoding UTF-8 is much more anarchistic than the one of the characters starting from A0h.
Nevertheless, other characters UTF-8, probably of the typographical characters Mac, are also converted when it is possible.

Since version 2.0 (and beta versions 1.9.2 and 1.9.3), Libremail analyzes the variable of environment $LANG to detect the character set (ISO-8859-n or UTF-8) used by the operating system.
The mails written with the same character set that that of the operating system are posted without conversion, the others are converted ISO-8859-1 with UTF-8 or UTF-8 with ISO-8859-15 to allow a good display of the accentuated characters.
In the same way, the seizure of the mails can be done as well with the character set ISO-8859-15 as the character set UTF-8 .

Encoding UTF-7 is not suported by Libremail.

Hour and time zone

For the display of the dates and hours of forwarding of the messages, Libremail did not take account of the time zones until version 2.1.4 .

Since version 2.2, the command vmailsj corrects the variations (in full hours) between the time zone of the sender and the time zone of the recipient and account it to make a chronological sorting of emails using of different time zones.
The tools being used to visualize the contents of the emails continue to display such as they are in the sender's emails dates and hours and the time zone of the sender.