As e -mail program (or e- mail client or mail client; technically Mail User Agent, abbreviated MUA ) refers to a program received with the e- mails, read, written and sent.
To view an e -mail, an e -mail program can either open directly on the mail server (usually via IMAP or IMAPS ) or by downloading from a mail server (usually via POP3 or POP3S ) and then open it locally, in the usually after it has been stored in a previously applied to user mailbox.
To send an e- mail sends the user's email program, these usually via the Simple Mail Transfer Protocol (SMTP) to an SMTP relay server (also smart host ), which they then send to the mail server of the recipient. The disadvantage of this method is that in the absence of availability of the relay server does not send e -mails is possible.
Alternatively, the shipment is via a locally available mail transfer agent can be specified (MTA ), with Linux or Unix sendmail interface has prevailed for even if other mail transfer agents such as qmail, Postfix, and Exim are used. This solution has the advantage of a local queue for outgoing e -mails and the disadvantage of a more complex installation.
An e -mail program needs to configure typically the following information that can be ascertained from the Internet Service Provider:
- Address of the server to read ( IMAP server ) or retrieving ( POP3 server ) the mails
- Username and password for the polling
- Address of the server to send (SMTP relay server ) to the mail
- Username and password to shipping
Frequently POP3 and SMTP server and the passwords are the same.
As the access to other user accounts on the Internet is recommended that you encrypt the data transfer types, see Transport Layer Security. Otherwise, the username and password can be intercepted; an attacker could read the e- mails or send e-mails via the user account. Since the beginning of 2014, freenet, t- online.de, GMX and WEB.de commit their users and users, only encrypted to receive or send emails.
The user of the program usually has more than one folder in which individual messages can be stored. Depending on the system and program are these folders actual subdirectories in the file system of the computer with individual files for each mail (see Maildir ) or archives in which multiple messages may be packed together to save memory. The archives can be executed again in " plain text " as text files (see mbox ) or as compressed archives, possibly the option of the user.
- Incoming mail is usually stored in an " inbox ". The user is shown as a list of the contents of the folder where the new, unread messages are highlighted and can be read individually. Some programs allow you to define rules by which mails are automatically distributed across multiple input folder.
- After reading - or when spam even before the opening of a single mail - allows the user to delete a mail, so it is moved to a " trash ", just like on the desktop of OS GUIs. As with the latter, the messages are therefore normally not deleted immediately, but only in a second step by emptying the Recycle Bin. Often, the user can choose, but also in the configuration that the second step is skipped.
- When a mail is to continue to be stored, the user can move it to " Archive Folders". It can create more than one of them to save for example private and business e-mails separately.
- In addition, there is often still a "Drafts " folder are stored in the pattern - mails that are to serve as a starting framework for create later mails. This land also mails that had created the user and actually wanted to send, then the latter but still broke, but the content already created would not discard completely.
- If the user has sent a mail, it is initially placed in an " output folder ", which is, so to speak, the FIFO memory to the physical mail delivery. At the level of this folder can be read so far as shipping is already advanced.
- The entries in the output folder will be re-stored after successful sending in a " Sent " folder, so that the user always has a receipt, which he has now sent exactly. The output folder so becomes gradually emptied.
The contents of each of these folders, the user can display in list form and mails read on the choice again, finally answer, use, delete or move or copy it to another folder as a starting structure for a newly created mail.
If the user has multiple user accounts, this folder structure is created, if necessary, separately for each account.
The user can instruct the program, if necessary, retrieve the mail server newly arrived mails to read them to answer it, forward it to send or delete them.