Send Mail from SUSE Linux(Gmail)

Mail from SUSE Linux to Gmail

In this, we will use Postfix as our MTA (mail transfer agent). 

1. Postfix is a free, open-source, actively maintained, and highly secure mail transfer agent.

2. Make sure port 25 and 587 is open or not.

3. In December of 1998, R. Gellens and J. Klensin submitted RFC 2476 in support of adding a new specification for internet email communications. The RFC proposed a split of the traditional massage submission and message relay concept. The RFC defined that message submission should occur over port 587 to ensure new policy and security requirements don't interfere with the traditional relay traffic over message relay port 25.

Note: All commands require root privileges.

1. Install Required Software

zypper update && zypper install postfix mailx cyrus-sasl

for other Linux flavor, we can change the word zypper  with the respected installer 

Note: Be sure with the administrator before updating…...

if your system is already updated just execute. 

zypper install postfix mailx cyrus-sasl

2. Configure Gmail Authentication 

Create or modify a password file that will be used by Postfix to establish authentication with Gmail. In the authentication information below, replace the username with your Gmail username and password with your Gmail password. If you are using a custom Gmail Apps domain name, you may replace gmail.com with your Google Apps domain.

The password file will reside in the Postfix configuration directory. The file can be named whatever you like, but the recommended filename is sasl_passwd.

Postfix configuration files reside in the directory /etc/postfix.

vim /etc/postfix/sasl_passwd

In this, I  used  vim file editor if u can use any other file editors also

[smtp.gmail.com]:587    username@gmail.com:password

replace the username with your Gmail username and the password with your Gmail password.

Save and close the file. Your Gmail password is stored as plaintext, so make the file accessible only by root:

 chmod 600 /etc/postfix/sasl_passwd

for the above command will change the file permeation to only by root/user

 3. Configure Postfix

There are six parameters which must be set in the Postfix configuration file: main.cf. The parameters are:

1. relayhost

2. smtp_use_tls

3. smtp_sasl_auth_enable

4. smtp_sasl_security_options

5. smtp_sasl_password_maps

6. smtp_tls_CAfile

Edit the main Postfix configuration file:

vim /etc/postfix/main.cf

modify the following values:

relayhost = [smtp.gmail.com]: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/ssl/ca-bundle.pem

Save and close the file.

It also requires that the Postfix master process configuration file master.cf be modified. Open it for editing:

vim /etc/postfix/master.cf

Locate the line below:

#tlsmgr unix - - n 1000? 1 tlsmgr

Uncomment it:

tlsmgr unix - - n 1000? 1 tlsmgr

Save and close the file.

4. Process Password File

postmap /etc/postfix/sasl_passwd

Then check it out /etc/postfix for the sasl_passwd.db file whether it was created or not.

 

5. Restart Postfix

systemctl restart postfix.service

for some version, this will works

postfix stop && postfix start

6. Enable "Less Secure Apps" In Gmail

You want to enable and disable settings refer to link

https://support.google.com/accounts/answer/6010255

7. Send A  Email

mail -s "Test subject" recipient@domain.com

You will be presented with a blank line (or a CC: field, which you can bypass by pressing Enter). Type the body of your message, pressing Enter for new lines. When you are finished composing the email, type CTRL-D to send it. To cancel the email, press CTRL-C twice.

To send a precomposed email, use the command:

mail -s "Subject Here" recipient@domain.com < textfile

Troubleshooting

If it's not working, check the logs for any Postfix errors:

journalctl

If you receive authentication errors from Gmail:

1. verify that Allow Less Secure Apps is turned on in your Gmail account settings

2. Verify that the password file sasl_passwd exists and  its contents are containing the correct information      

3. restart Postfix.

If you see any TLS errors :

1. check the configuration in main.cf 

2. If you make any configuration changes, restart Postfix  

If u get any unreachable errors:

      1.ensure the internet service provider(ISP) is allowing or blocking the service.

      2.check the iptables outbound rules if any port is blocked by the iptable.