обрабатывать сообщения (process messages)
Использование в приложениях (Application usage)
Delivery of messages to remote systems requires the existence of
communication paths to such systems. These need not exist.
Input lines are limited to {LINE_MAX} bytes, but mailers between
systems may impose more severe line-length restrictions. This
volume of POSIX.1‐2017 does not place any restrictions on the
length of messages handled by mailx, and for delivery of local
messages the only limitations should be the normal problems of
available disk space for the target mail file. When sending
messages to external machines, applications are advised to limit
messages to less than 100000 bytes because some mail gateways
impose message-length restrictions.
The format of the system mailbox is intentionally unspecified.
Not all systems implement system mailboxes as flat files,
particularly with the advent of multimedia mail messages. Some
system mailboxes may be multiple files, others records in a
database. The internal format of the messages themselves is
specified with the historical format from Version 7, but only
after the messages have been saved in some file other than the
system mailbox. This was done so that many historical
applications expecting text-file mailboxes are not broken.
Some new formats for messages can be expected in the future,
probably including binary data, bit maps, and various multimedia
objects. As described here, mailx is not prohibited from handling
such messages, but it must store them as text files in secondary
mailboxes (unless some extension, such as a variable or command
line option, is used to change the stored format). Its method of
doing so is implementation-defined and might include translating
the data into text file-compatible or readable form or omitting
certain portions of the message from the stored output.
The discard and ignore commands are not inverses of the retain
command. The retain command discards all header-fields except
those explicitly retained. The discard command keeps all header-
fields except those explicitly discarded. If headers exist on the
retained header list, discard and ignore commands are ignored.
