You may be able to use following special URL strings for some browsers to confirm their settings.

Debian offers many free browser plugin packages in the main component which can handle not only Java (software platform) and Flash but also MPEG, MPEG2, MPEG4, DivX, Windows Media Video (.wmv), QuickTime (.mov), MP3 (.mp3), Ogg/Vorbis files, DVDs, VCDs, etc. Debian also offers helper programs to install non-free browser plugin packages as contrib or non-free components.

Some web sites refuse to be connected based on the user-agent string of your browser. You can work around this situation by spoofing the user-agent string. For example, you can do this by adding following line into user configuration files such as "~/.gnome2/epiphany/mozilla/epiphany/user.js" or "~/.mozilla/firefox/*.default/user.js".

user_pref{"general.useragent.override","Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)"};

Alternatively, you can add and reset this variable by typing "about:config" into URL and right clicking its display contents.

In order to contain spam (unwanted and unsolicited e-mail) problems, many ISPs which provide consumer grade Internet connection are implementing counter measures.

When configuring your mail system or resolving mail delivery problems, you must consider these new limitations.

In light of these hostile Internet situation and limitations, some independent Internet mail ISPs such as Yahoo.com and Gmail.com offer the secure mail service which can be connected from anywhere on the Internet using Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL).

The most simple mail configuration is that the mail is sent to the ISP's smarthost and received from ISP's POP3 server by the MUA (see Section 6.4, “Mail user agent (MUA)”) itself. This type of configuration is popular with full featured GUI based MUA such as icedove(1), evolution(1), etc. If you need to filter mail by their types, you use MUA's filtering function. For this case, the local MTA (see Section 6.3, “Mail transport agent (MTA)”) need to do local delivery only.

The alternative mail configuration is that the mail is sent via local MTA to the ISP's smarthost and received from ISP's POP3 by the mail retriever (see Section 6.5, “The remote mail retrieval and forward utility”) to the local mailbox. If you need to filter mail by their types, you use MDA with filter (see Section 6.6, “Mail delivery agent (MDA) with filter”) to filter mail into separate mailboxes. This type of configuration is popular with simple console based MUA such as mutt(1), gnus(1), etc., although this is possible with any MUAs (see Section 6.4, “Mail user agent (MUA)”). For this case, the local MTA (see Section 6.3, “Mail transport agent (MTA)”) need to do both smarthost delivery and local delivery.

For the Internet mail via smarthost, you (re)configure exim4-* packages as the following.

$ sudo /etc/init.d/exim4 stop
$ sudo dpkg-reconfigure exim4-conf

Chose "mail sent by smarthost; received via SMTP or fetchmail".

Set "IP address or host name of the outgoing smarthost:" to "smtp.hostname.dom:587".

Reply to "Keep number of DNS-queries minimal (Dial-on-Demand)?" as one of the following.

Create password entries for the smarthost by editing " /etc/exim4/passwd.client"

$ sudo vim /etc/exim4/passwd.client
 ...
$ cat /etc/exim4/passwd.client
^smtp.*\.hostname\.dom:username@hostname.dom:password

Start exim4 by the following.

$ sudo /etc/init.d/exim4 start

The host name in "/etc/exim4/passwd.client" should not be the alias. You check the real host name with the following.

$ host smtp.hostname.dom
smtp.hostname.dom is an alias for smtp99.hostname.dom.
smtp99.hostname.dom has address 123.234.123.89

I use regex in "/etc/exim4/passwd.client" to work around the alias issue. SMTP AUTH probably works even if the ISP moves host pointed by the alias.

For the Internet mail via smarthost, you should first read postfix documentation and key manual pages.

You (re)configure postfix and sasl2-bin packages as follows.

$ sudo /etc/init.d/postfix stop
$ sudo dpkg-reconfigure postfix

Chose "Internet with smarthost".

Set "SMTP relay host (blank for none):" to "[smtp.hostname.dom]:587" and configure it by the following.

$ sudo postconf -e 'smtp_sender_dependent_authentication = yes'
$ sudo postconf -e 'smtp_sasl_auth_enable = yes'
$ sudo postconf -e 'smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd'
$ sudo postconf -e 'smtp_sasl_type = cyrus'
$ sudo vim /etc/postfix/sasl_passwd

Create password entries for the smarthost.

$ cat /etc/postfix/sasl_passwd
[smtp.hostname.dom]:587     username:password
$ sudo postmap hush:/etc/postfix/sasl_passwd

Start the postfix by the following.

$ sudo /etc/init.d/postfix start

Here the use of "[" and "]" in the dpkg-reconfigure dialog and "/etc/postfix/sasl_passwd" ensures not to check MX record but directly use exact hostname specified. See "Enabling SASL authentication in the Postfix SMTP client" in "usr/share/doc/postfix/html/SASL_README.html".

There are a few mail address configuration files for mail transport, delivery and user agents.

The mailname in the "/etc/mailname" file is usually a fully qualified domain name (FQDN) that resolves to one of the host's IP addresses. For the mobile workstation which does not have a hostname with resolvable IP address, set this mailname to the value of "hostname -f". (This is safe choice and works for both exim4-* and postfix.)

When setting the mailname to "hostname -f", the spoofing of the source mail address via MTA can be realized by the following.

For postfix, the following extra steps are needed.

# postmap hash:/etc/postfix/generic
# postconf -e 'smtp_generic_maps = hash:/etc/postfix/generic'
# postfix reload

You check filters using the following.

There are several basic MTA operations. Some may be performed via sendmail(1) compatibility interface.

Customize "~/.muttrc" as the following to use mutt as the mail user agent (MUA) in combination with vim.

# use visual mode and "gq" to reformat quotes
set editor="vim -c 'set tw=72 et ft=mail'"
#
# header weeding taken from the manual (Sven's Draconian header weeding)
#
ignore *
unignore from: date subject to cc
unignore user-agent x-mailer
hdr_order from subject to cc date user-agent x-mailer
set hostname=spoof.example.org
set from="First Last <username@example.org>"
....

Add the following to "/etc/mailcap" or "~/.mailcap" to display HTML mail and MS Word attachments inline.

text/html; lynx -force_html %s; needsterminal;
application/msword; /usr/bin/antiword '%s'; copiousoutput; description="Microsoft Word Text"; nametemplate=%s.doc

getmail(1) configuration is described in getmail documentation. Here is my set up to access multiple POP3 accounts as user.

Create "/usr/local/bin/getmails" as the following.

#!/bin/sh
set -e
rcfiles="/usr/bin/getmail"
for file in $HOME/.getmail/config/* ; do
  rcfiles="$rcfiles --rcfile $file"
done
exec $rcfiles $@

Configure it as the following.

$ sudo chmod 755 /usr/local/bin/getmails
$ mkdir -m 0700 $HOME/.getmail
$ mkdir -m 0700 $HOME/.getmail/config
$ mkdir -m 0700 $HOME/.getmail/log

Create configuration files "$HOME/.getmail/config/pop3_name" for each POP3 accounts as the following.

[retriever]
type = SimplePOP3SSLRetriever
server = pop.example.com
username =  pop3_name@example.com
password = secret

[destination]
type = MDA_external
path = /usr/bin/maildrop
unixfrom = True

[options]
verbose = 0
delete = True
delivered_to = False
message_log = ~/.getmail/log/pop3_name.log

Configure it as the following.

$ chmod 0600 $HOME/.getmail/config/*

Schedule "/usr/local/bin/getmails" to run every 15 minutes with cron(8) by executing "sudo crontab -e -u <user_name>" and adding following to user's cron entry.

5,20,35,50 * * * * /usr/local/bin/getmails --quiet

fetchmail(1) configuration is set by "/etc/default/fetchmail", "/etc/fetchmailrc" and "$HOME/.fetchmailrc". See its example in "/usr/share/doc/fetchmail/examples/fetchmailrc.example".

maildrop(1) configuration is described in maildropfilter documentation. Here is a configuration example for "$HOME/.mailfilter".

logfile $HOME/.maildroplog
# clearly bad looking mails: drop them into X-trash and exit
if (    /^X-Advertisement/ ||\
        /^Subject:.*BUSINESS PROPOSAL/ ||\
        /^Subject:.*URGENT.*ASISSTANCE/ ||\
        /^Subject: *I NEED YOUR ASSISTANCE/ )
    to "$HOME/Maildir/X-trash/"

# Delivering mailinglist messages
if (    /^Precedence:.*list/ ||\
        /^Precedence:.*bulk/ ||\
        /^List-/ ||\
        /^X-Distribution:.*bulk/ )
{
    if (    /^Resent-Sender.*debian-user-request@lists.debian.org/)
        to "$HOME/Maildir/debian-user/"
    if (    /^Resent-Sender.*debian-devel-request@lists.debian.org/)
        to "$HOME/Maildir/debian-devel/"
    if (    /^Resent-Sender.*debian-announce-request@lists.debian.org/)
        to "$HOME/Maildir/debian-announce/"
    to "$HOME/Maildir/mailing-list/"
}
to "$HOME/Maildir/Inbox/"
exit

Here is an equivalent configuration with "$HOME/.procmailrc" for procmail(1).

MAILDIR=$HOME/Maildir
DEFAULT=$MAILDIR/Inbox/
LOGFILE=$MAILDIR/Maillog
# clearly bad looking mails: drop them into X-trash and exit
:0
* 1^0 ^X-Advertisement
* 1^0 ^Subject:.*BUSINESS PROPOSAL
* 1^0 ^Subject:.*URGENT.*ASISSTANCE
* 1^0 ^Subject: *I NEED YOUR ASSISTANCE
X-trash/

# Delivering mailinglist messages
:0
* 1^0 ^Precedence:.*list
* 1^0 ^Precedence:.*bulk
* 1^0 ^List-
* 1^0 ^X-Distribution:.*bulk
{
:0
* 1^0 ^Return-path:.*debian-devel-admin@debian.or.jp
jp-debian-devel/

:0
* ^Resent-Sender.*debian-user-request@lists.debian.org
debian-user/

:0
* ^Resent-Sender.*debian-devel-request@lists.debian.org
debian-devel/

:0
* ^Resent-Sender.*debian-announce-request@lists.debian.org
debian-announce

:0
mailing-list/
}

:0
Inbox/

You need to manually deliver mails to the sorted mailboxes in your home directory from "/var/mail/<username>" if your home directory became full and procmail(1) failed. After making disk space in the home directory, run the following.

# /etc/init.d/${MAILDAEMON} stop
# formail -s procmail </var/mail/<username>
# /etc/init.d/${MAILDAEMON} start

SSH has two authentication protocols.

See "/usr/share/doc/ssh/README.Debian.gz", ssh(1), sshd(8), ssh-agent(1), and ssh-keygen(1) for details.

Following are the key configuration files.

The following starts an ssh(1) connection from a client.

If you use the same user name on the local and the remote host, you can eliminate typing "username@". Even if you use different user name on the local and the remote host, you can eliminate it using "~/.ssh/config". For Debian Alioth service with account name "foo-guest", you set "~/.ssh/config" to contain the following.

Host alioth.debian.org svn.debian.org git.debian.org
    User foo-guest

For the user, ssh(1) functions as a smarter and more secure telnet(1). Unlike telnet command, ssh command does not bomb on the telnet escape character (initial default CTRL-]).

To establish a pipe to connect to port 25 of remote-server from port 4025 of localhost, and to port 110 of remote-server from port 4110 of localhost through ssh, execute on the local host as the following.

# ssh -q -L 4025:remote-server:25 4110:remote-server:110 username@remote-server

This is a secure way to make connections to SMTP/POP3 servers over the Internet. Set the "AllowTcpForwarding" entry to "yes" in "/etc/ssh/sshd_config" of the remote host.

One can avoid having to remember passwords for remote systems by using "RSAAuthentication" (SSH-1 protocol) or "PubkeyAuthentication" (SSH-2 protocol).

On the remote system, set the respective entries, "RSAAuthentication yes" or "PubkeyAuthentication yes", in "/etc/ssh/sshd_config".

Generate authentication keys locally and install the public key on the remote system by the following.

$ ssh-keygen
$ cat .ssh/identity.pub | ssh user1@remote "cat - >>.ssh/authorized_keys"

$ ssh-keygen -t rsa
$ cat .ssh/id_rsa.pub | ssh user1@remote "cat - >>.ssh/authorized_keys"

$ ssh-keygen -t dsa
$ cat .ssh/id_dsa.pub | ssh user1@remote "cat - >>.ssh/authorized_keys"

There are some free SSH clients available for other platforms.

It is safer to protect your SSH authentication secret keys with a pass phrase. If a pass phrase was not set, use "ssh-keygen -p" to set it.

Place your public SSH key (e.g. "~/.ssh/id_rsa.pub") into "~/.ssh/authorized_keys" on a remote host using a password-based connection to the remote host as described above.

$ ssh-agent bash
$ ssh-add ~/.ssh/id_rsa
Enter passphrase for /home/<username>/.ssh/id_rsa:
Identity added: /home/<username>/.ssh/id_rsa (/home/<username>/.ssh/id_rsa)

No remote password needed from here on for the next command.

$ scp foo <username>@remote.host:foo

Press ^D to terminating ssh-agent session.

For the X server, the normal Debian startup script executes ssh-agent as the parent process. So you only need to execute ssh-add once. For more, read ssh-agent(1)and ssh-add(1).

You need to protect the process doing "shutdown -h now" (see Section 1.1.8, “How to shutdown the system”) from the termination of SSH using the at(1) command (see Section 9.5.13, “Scheduling tasks once”) by the following.

# echo "shutdown -h now" | at now

Running "shutdown -h now" in screen(1) (see Section 9.1, “The screen program”) session is another way to do the same.

If you have problems, check the permissions of configuration files and run ssh with the "-v" option.

Use the "-P" option if you are root and have trouble with a firewall; this avoids the use of server ports 1 — 1023.

If ssh connections to a remote site suddenly stop working, it may be the result of tinkering by the sysadmin, most likely a change in "host_key" during system maintenance. After making sure this is the case and nobody is trying to fake the remote host by some clever hack, one can regain a connection by removing the "host_key" entry from "~/.ssh/known_hosts" on the local host.