Category Archives: Howto Tutorials (EN)

Howto Tutorials English Contribution Howto’s and Tutorials technical contribution for Professionals

How to Forward Mails to Gmail using Postfix

Send email using Postfix (MTA) Mail Transfer Agent via Gmail Relayhost

Emails sending with Postfix (MTA) Mail Transfer Agent via Gmail relay host. E-mails are delivered via Gmail account, the clients in the local network use Postfix as a local SMTP gateway. This tutorial shows how to do this.

In situations with these, for example, multifunctional devices, or apps that do not support authentication via Mail Submission and STARTTLS (port 587), e-mails can send via local Postfix MTA without the need to log on to a mail server.

If CentOS Linux is used, the required packages are installed as root.

yum update && yum install -y postfix mailx cyrus-sasl cyrus-sasl-plain

On a Debian and Ubuntu, the package installation is as follows.

apt-get update && apt-get install -y postfix mailutils

The Postfix configuration is to be edited by opening the file /etc/postfix/

mynetworks =
myhostname =
mydestination = $myhostname, localhost.$mydomain, localhost
inet_interfaces = all
inet_protocols = ipv4
relayhost = []:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options =
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt

Enter the local networks in mynetworks. As myhostname the PTR resource record that can be resolved on the Internet for determining the PTR entry, the following command can be executed in the terminal, as in the following example, or here.

$ curl -s | xargs host domain name pointer

Next, a /etc/postfix/sasl_passwd file is created with the following content.


Instead of use your own Gmail account, with password the Google password.

Use postmap to create the file sasl_passwd as Berkeley DB.

postmap /etc/postfix/sasl_passwd

Hint. Run postmap after each change.

Now Postfix is restarted to activate the configuration.

systemctl restart postfix

Test the Postfix configuration with this line in the terminal.

echo "Here is a text." | mail -v -s "Test subject" -r

The be the valid Gmail address, and if, enter a valid recipient email.

Note. This Google Account requires disabled settings under Security – Sign in to Google – go to Security Verification and set two factor Off, and access to the Google Account when accessed by less secure apps must be On.

Postfix logging with syslog in the log file /var/log/maillog in which you can check whether the e-mail was sent and accepted by

tail -25 /var/log/maillog

Use mailq to check the queue for any rejected mails.

If you find authentication errors in maillog, the Google Account security settings must be checked.

status=deferred (SASL authentication failed; server[] said: 534-5.7.9 Application-specific password required. Learn more at?534 5.7.9

Hint. It can happen that after several sending attempts, then rejected (bounced) mails are in the queue, the command mailq gets them, with postsuper -d you remove mails from the queue.

postsuper -d ALL

Forward postfix alias to dev-null

Postfix Virtual Alias do-not-reply Forwarding to /dev/null

In situations with these e-mail addresses of type “do-not-reply” are sent, where the mailbox would have to be sweep at regular intervals, or if the mailbox does not exist at all, there is the easy way for incoming e-mails to use a postfix alias and virtual alias with forwarding to the null device – /dev/null.

The usual solution is by forwarding to /dev/null. In a local setup, this can be done in /etc/aliases.

do-not-reply: /dev/null

However, when virtual postfix domains are used, it becomes a bit more expensive. For virtual domain users, e-mail cannot be forwarded to a file. It must go to a user or an email address, for which an alias user is added in /etc/aliases.

devnull: /dev/null

After that, the new alias will be add to the aliases.db.

$ newaliases

The alias points to a Virtual Domain Alias in /etc/postfix/virtual. devnull

Note: By default, the Sendmail aliases located under /etc, for Postfix aliases is often copied under /etc/postfix, to make sure what is defined in /etc/postfix/ is at alias_maps.

alias_maps = hash:/etc/aliases
alias_maps = hash:/etc/postfix/aliases

After that run postmap.

$ postmap /etc/postfix/virtual

and activates the Postfix change.

$ postfix reload

How do you know if the change works!

The following command can be used to verify that the alias has been set up correctly.

$ postmap -q /etc/postfix/virtual

The following output should be made.


Disable VIM copy paste Insert Visual Mode

VIM Visual Mode — (insert) VISUAL — Disable when inserting with right-click

Vi Improved is the universal tool for many admins and developers in the Unix world in their daily tasks. The powerful editor with regular expressions, especially established in Unix operating systems, can count on so many followers.

Vim also learns the porting for Windows, which is probably more interesting for those who move in the parallel universe, Linux and Windows. For beginners, however, the entry of the uncommon editor means greater hurdles in familiarization. But also Vim professionals facing new features, because Vim is also constantly being further developed, so there is the compatibility mode and, for some time, the visual block mode, which is enabled with CTRL-V.

Figure: Vim Visual Block Mode (Ctrl+V) when inserting with mouse right-click.

The symptom is that the Vim blockwise visual mode (CTRL-V) collides when inserting using right-click with the mouse or a trackpad.

A personal .vimrc can enable the compatibility to the classic vi, also the mouse control can by disabled. If you would insert with right-click then use the option set mouse-=a.

$ echo "set compatible" > ~/.vimrc
$ echo "set mouse-=a" >> ~/.vimrc

NOTE: that ~/.vimrc Vim automatically enables nocompatible mode as soon as a personal initialization file is available.

debian.vim sets nocompatible. Setting compatible changes numerous options, so any other options should be set AFTER setting compatible.

The — VISUAL BLOCK — mode differs from the normal VISUAL mode in which after completing the command you automatically return to the normal insert mode. When editing you go with CTRL-V in the VISUAL BLOCK mode.

To insert the previously yanked (y) or deleted (d) text in Visual Block mode, enter (p) for insert in normal mode.

The Vim Compatibility Mode

Compatible mode means vi compatibility with the old vi with :set compatible,which disables all improvements and innovations of Vi Improved. This is not recommended, but some systems (mainly for backward compatibility with old Unix systems) offer the vi command implemented with Vim in compatible mode.

Vim Visual Mode Rerference Manual – Vim Version 7.3