Fix SMTP error 421, 451

Well, you might be receiving an error message while sending an email to your recipient in the form of a three-digit number, each containing a detail about the server or an answer to a command. First, try restarting the mail server but if it keeps coming up follow the steps below. So let’s see how to fix SMTP error 421, 451:

421 SMTP Server error: too many concurrent sessions

SMTP error 421 denotes either a temporary problem on the mail server or a problem with the recipient's email account.

If you reached a limit (restriction) on your mail account you may get a 421 error as some mail providers might return this error.

Depending on the cause we will see how to fix SMTP error 421. You need to try each below solution until it’s fixed.

Solution1: Fix the Outlook Configuration Issues

If this issue is caused right after the configuration of the outlook account, then the error is occurred due to a configuration mistake. The invalid port number setting or mail server name will show “421 cannot connect to SMTP Server” error while sending or receiving an email so remove the email account and add the account again.

To add the configuration correctly follow the below steps:
Step 1 - Open Outlook account and go to File > Account Setting, Select the email account and click Remove button.
Step 2- Once the account is removed, click the New button then select the Email account and enter the required information. Click Next and wait for the settings to be configured and check the test mail sent.
Step 3- If the test email delivered successfully, then your account is configured properly. In case, if you face the same error then follow Solution2.

Solution2: Change the SMTP port number

When you enter a wrong SMTP port number you will end up receiving an SMTP 421 error. You can check by changing the SMTP port number from Port 25 to 465 and see if the normal functionality resumes. 
For this you need to go to File > Account Settings, then choose the email account that’s affected and click on the Change button.
In the Change Account window, select More Settings > Advanced tab and now set to 465 in modify the Outgoing server (SMTP).
Ensure ‘Use the following type of encrypted connection: is set to SSL ‘.

Solution3: Check 3rd party firewall interference

Though the firewall protects us against malicious attacks, it can block certain IP ranges, so let’s test by disabling 3rd party firewall and send a test mail.
For that Open the Control Panel > under Programs and Features section choose your 3rd -party antivirus and uninstall it. Then check by restarting your PC.
You can install the firewall from the official site and re-check the error by sending a test mail.

Solution4: Check VPN interference

Try sending a test mail once after you disable your VPN connection, if the mail is sent successfully, then the VPN will be the cause of the error. If the error persists you might probably need to contact the VPN network support and ask to whitelist the email server.

SMTP error 451 Exchange Server Error

Next, we will see how to fix SMTP error 451. When you face issues as mail limits exceeded, DNS errors, unreachable mail servers, etc., the Email Relay environment will get affected due to a temporary exchange server. This 451 server error can be due to a discrepancy on Sender or Receiver Exchange server. Let’s see how to resolve the 451 server error.

Step to resolve Exchange Server Error 451

Inspect Queue Viewer

• Open Exchange Management Console > Click Edge Transport server.
• Then go to toolbox > Queue Viewer.
• Select Mail Flow tools > Queue Viewer tool.
• 
  

Verify DNS Configuration

• Login to the Edge Transport server locally and use Console Switch, if you are accessing “Remote Desktop Connection”.
• Next, open Exchange Management Console > Edge Transport Server > properties.
• Then go to Internal DNS Lookups and check whether it is in Default Configuration Setting. If not, set it to Default.
• 
  

Implementing Internal and External Lookups

1. Internal Lookups
When you have multiple network adapters, you need to go with an Internal Network Card and then choose the card to access the DNS setting. If any misconfiguration occurs, it will allow all the IP addresses to modify.
If there is no IP address detected, then the NIC card might not be configured with DNS server entries. Therefore fill the card with appropriate details and confirm the configuration.   

 
2. External Lookups
If you are using a single network card with public DNS, modification of configuration may affect external resolution and it might stop the email flow.

Command Line tools to test DNS Server

NSLOOKUP – To get DNS records that hold Server & IP address Information.
TELNET – To test ports.


Locate IP Address of the Server

• First, type “nslookup” to find a server IP address and click to open the NSLOOKUP tool.
• Next, type set type=mx and press enter.
• Finally, enter the domain name you wish to extract the MX record and hit enter.
• 
  

Check out SMTP connection Via TELNET command

• Open Command Prompt (cmd) and enter telnet.
• Enter set logfile (location:/filename)
• Next, type open mail.abc.com 25 and press enter.
• Now type the command EHLO contoso.com and execute it.
• Compose test email message with parameters like from, receive, notify, data and subject.
• After the process termination, it will generate a success or failure confirmation report.
• 
  

Hope you would have fixed. If the issue still persists or any other email error Try Expert Solution.
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Hybrid Cloud – The key survival in today’s business

Cloud technologies are one of the mainstream options in the IT world and global enterprises have already migrated into cloud computing. Due to a lack of control and privacy, opting to go fully on the public cloud will not be the best for IT infrastructure. So if your enterprise is looking for the benefits of both Public and Private Cloud, then the best option would be a hybrid cloud.

‘’ Right Scale survey estimation indicates that enterprises with a hybrid cloud strategy have grown to 58% in 2020, up from 51% in 2018. It also says that 28% of enterprises who haven't yet adopted hybrid cloud consider it a priority to do so.’’

Now you might wonder why hybrid cloud is heading, the main reasons is its Simplicity, Security and Collaboration. As we know it’s not going to be an overnight success, but you can expect cost savings and increased operational efficiency if it is deployed properly.
Few companies are deviating from building their own data centers, as they can create one in the cloud with a few clicks of a mouse. Let us see what are the main advantage of adopting hybrid cloud systems for enterprises.

Key Benefits of Hybrid Cloud:

•          Security

When compared to other public clouds, the Hybrid cloud has a key potential to increase the security level. Using a hybrid cloud, companies can decide which applications or services can be stored in public and private clouds.  This helps you to keep all your sensitive data on a highly secured dedicated infrastructure. The proper integration of public and private cloud will play a better role in strengthening the security level. It also ensures the cloud space from overburdening. Therefore it provides end-to-end security for the data stored.

•          Cost-Effective

A hybrid cloud follows a pay-as-you-need model that is, you only have to pay for resources that you use. It offers you the flexibility to manage costs without comprising the quality of services i.e., its reduction in your Total Cost of Ownership (TCO). 
 

•          More flexibility

As we know flexibility is one of the core advantages that enterprises look for in the cloud environment. The hybrid infrastructure is designed in such a way that you get maximum efficiency and scalability.
You can choose where to put your applications, where they can run best etc., by providing a more way for flexibility than before. It combines the security of a private cloud with the scalability of a public cloud to meet your specific requirements.

Wrapping up:

In the upcoming days, hybrid cloud models will focus on keeping your core systems in place while using cloud applications to ‘innovate around the edges’. Being selective in choosing the right technology cloud players is key. When it’s used properly, Hybrid models can modernize and will be future-proof existing technology for your organization.

You can check our latest blog on: Run multiple PHP versions on the same server

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Run multiple PHP versions on the same server

You would have faced the trouble of keep swapping the PHP version depending on the task in hand you need to use. With this solution, you can install multiple PHP versions in the system and make them work simultaneously.
To run two or more PHP versions for different sites on the same LAMP stack by using mod_fcgid to create a .fcgi wrapper script.  The script forwards all the PHP requests which were made from php-cgi binary.
Considering a server running on PHP 7.2  where a specific site requires an older PHP version (eg PHP 5.6)

Required Installation Packages

The php56-php packages are in the Remi repos and they install to /opt/remi/
In order to create the PHP wrapper script, mod_fcgid Apache module needs to be installed.
[root@server ~]#yum install php56-php php56-php-pear mod_fcgid

Remove alternate PHP configuration(s)

A configuration file to load PHP 5.6 would be created  into Apache at /etc/httpd/conf.d/php56-php.conf, which has to be DELETED else it would conflict with the existing PHP version and would fail Apache  to start.
[root@server ~]#rm -f /etc/httpd/conf.d/php56-php.conf

PHP wrapper script creation

This script will set the environment for the specific PHP versions. (here PHP 5.6)
Example path of a specified site '/var/www/www.actsupport.com/cgi-bin/php56.fcgi'
(name the script depending on the PHP version)

[root@server ~]#cd /var/www/www/actsupport.com/cgi-bin
[root@server ~]#vim php56.fcgi
#!/bin/sh
PHPRC=/opt/remi/php56/root/etc/
export PHPRC
export PHP_FCGI_MAX_REQUESTS=5000
export PHP_FCGI_CHILDREN=16
exec /opt/remi/php56/root/usr/bin/php-cgi

[root@server ~]#chmod +x /var/www/www.actsupport.com/cgi-bin/php56.fcgi
PHPRC is the path of the folder for php.ini and the exec is the full path to the php-cgi binary of the enabling PHP version, Update the values on your environment accordingly.

Update Apache Configuration

Append the Virtual Host for the specific domain on the question.
[root@server ~]#/etc/httpd/sites-available/actsupport.com.conf (Generic/Custom path based on the environment)
<IfModule mod_fcgid.c>
    RemoveHandler .php
    RemoveType application/x-httpd-php
    Action application/x-httpd-php5 /cgi-bin/php56.fcgi
    AddType application/x-httpd-php5 .php
    AddHandler application/x-httpd-php5 .php
</IfModule>

HTTPS config to be updated, if applicable
EDIT PHP config

Modify by commenting out the <FilesMatch> and SetHandler block because it can't be overridden by the RemoveHandler directive we added to the site's virtualhost entry.
It is being replaced with an AddHandler directive that performs the same purpose but will respect being overridden.

[root@server ~]#/etc/httpd/conf.d/php.conf
#    <FilesMatch \.php$>
#        SetHandler application/x-httpd-php
#    </FilesMatch>
       AddHandler application/x-httpd-php .php

PHP Modules Installation

The required PHP modules vary based on the site and if we restart Apache now, the alternate PHP version would run without the necessary modules and be incompatible accordingly. Though very few modules being installed by default the below list works in many setups. However, install other PHP modules that are needed as necessary and make sure to install the phpXX-php-* versions from the Remi Repo for any PHP versions used to avoid accidental module installation for the wrong PHP versions of human error prefix.
php56-php-gd
php56-php-mbstring
php56-php-xml
php56-php-mysqlnd
php56-php-mssql
php56-php-ioncube-loader

To install the above use
[root@server ~]#yum install php56-php-gd php56-php-mbstring php56-php-xml php56-php-mysqlnd php56-php-mssql php56-php-ioncube-loader

Also make sure the php.ini for the specific PHP version is probably located at /opt/remi/phpXX/root/etc/php.ini.

Finally restart Apache

Finally, you need to restart Apache
[root@server ~]#service httpd restart

Verify PHP changes

Create a info.php page and verify changes.
[root@server ~]#vim info.php
<?php
phpinfo:();
?>

I hope you have resolved the issue related to multiple PHP versions. If you need any assistance Contact Us.

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Steps to Install Jira on Centos7

The bug-tracking tool Jira will track issues and bugs related to your software and Mobile apps. It is developed by an Australian Company Atlassian. You can manage your project easily, as Jira dashboard consists of many useful functions and features which make handling of the issue easily.

Now let’s see how to install and configure latest version of Jira on centos7

Steps to Install & Configure:

Install JIRA on Centos7
To establish Jira, you must require JAVA software package. So, First you need to check the Java package and its version by “JAVA – version” Command.

# yum install
java-1.8.0-openjdk java-1.8.0-openjdk-devel
# java -version
openjdk version "1.8.0_212"

Let's Install MySQL Database

Install and configure MySQL to start on system boot & set password.

# wget https://dev.mysql.com/get/mysql57-community-release-el7-11.noarch.rpm
# rpm -ivh mysql57-community-release-el7-11.noarch.rpm
# yum install mysql-server
# systemctl start mysqld
# systemctl status mysqld
# grep 'temporary password' /var/log/mysqld.log  ## to get default password ##
# mysql_secure_installation    ## use default password and change new password ##

Note: You have to set a strong password with uppercase, lowercase letters, numbers and special characters etc.

Now create MySQL Database and user for Jira with following commands:

# mysql -u root -p
CREATE DATABASE jiradb CHARACTER SET utf8 COLLATE utf8_bin;
grant all privileges on jiradb.* to 'jira'@'%' identified by 'password';
flush privileges

You should maintain a strong password otherwise you will get below error:

ERROR 1819 (HY000): This shows that your password does not satisfy the current policy requirements
For a simple password use below command in mysql prompt
SET GLOBAL validate_password_policy=LOW;
Now it allows to keep simple password.

Next exit from MySQL and then restart MySQL service as shown below

# systemctl restart mysqld

Installation of JIRA
To install Jira on centos7. Download the latest version of JIRA installer from: https://www.atlassian.com/software/jira/download

# cd /opt
# wget https://www.atlassian.com/software/jira/downloads/binary/atlassian-jira-software-8.6.0.zip

Then, Execute the .zip file and install JIRA.

# unzip atlassian-jira-software-8.2.0.zip 
# mv atlassian-jira-software-8.2.0-standalone atlasian
# mkdir /opt/jira
# mkdir /opt/jira/home
# vi /opt/atlassian/atlassian-jira/WEB-INF/classes/jira-application.properties
### set jira.home as jira.home = /opt/jira/home ###
# cd /opt/atlassian/bin
# ./startup.sh

Once after completing the Jira Installation. You can now access Jira as http://ip_address:8080

To Copy the MySQL JDBC Driver
Download jdbc drivers from http://dev.mysql.com/downloads/connector/j/

You can either download .tar.gz or .zip file and copy the MySQL JDBC driver to application server file as shown:

# cd mysql-connector-java-5.1.47
# mv mysql-connector-java-5.1.47.jar /opt/atlassian/lib/

To Restart Jira service

# cd /opt/atlassian/bin/
# ./stop-jira.sh
# ./start-jira.sh

Hope it helps. If you need any assistance Contact Us

Read our existing blog post : Steps to install PhantomJS On CentOS7

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Check Iptables Firewall set up on Centos 6

You can use Iptables to secure your Linux server or VPS. With Iptables you can monitor the traffic of your server using tables, which are a set of rules called chains. Iptables is a flexible firewall tool and few tricks and commands could make working with Iptables much easier.

To configure firewall rules for IPv6, you will have to set up the ip6tables service. If you are using CentOS 7, you will need to set up your firewall using firewalld.

Now lets see how to create a simple firewall on a Centos VPS:

Decide the services and ports to open

Once you have choosed the port to be opened, all other unnecessary ports will be blocked.
You are going to leave SSH port open so that you can connect to the VPS remotely:
let’s say, port 22.
For web traffic open port 80 and 443. To send email, open port 25 (regular SMTP) and 465 (secure SMTP) and to receive open the usual port 110 (POP3) and 995 (secure POP3 port).

Block comman attacks using iptables

You can block common network attacks with the help of iptables ; We will discuss few  attacks:

- >To block null packets use the below command

iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP

-> To reject is a syn-flood attack you can use

iptables -A INPUT -p tcp ! --syn-m state --state NEW -j DROP

Note:

–i  : Insert a rule
-A : Append
-j   : option specifies the target if a rule is matched

-> To block XMAS packets

iptables -A INPUT -p tcp
--tcp-flags ALL ALL -j DROP

The server allocates a large number of resources for this packet, as it requires more processing than the usual packets.

Add selected services

Open the ports for your selected services and start adding to the firewall filter. Let’s start with localhost interface:

iptables -A INPUT -i lo -j ACCEPT

This command tells iptables to add a rule to the incoming filter table (INPUT) and accept (-j ACCEPT) the traffic that comes via the localhost interface.

Next you can allow web server traffic by adding the two ports to ACCEPT the change.

iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

Then you can allow users to use your SMTP servers, using:

iptables -A INPUT -p tcp -m tcp --dport 25 -j ACCEPT
iptables -A INPUT -p tcp -m tcp --dport 465 -j ACCEPT

This command will allow users to read email on their server which allow POP3 traffic

iptables -A INPUT -p tcp -m tcp --dport 110 -j ACCEPT
iptables -A INPUT -p tcp -m tcp --dport 995 -j ACCEPT

Next you can allow IMAP mail protocol:

iptables -A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
iptables -A INPUT -p tcp -m tcp --dport 993 -j ACCEPT

Limiting SSH access

To allow SSH traffic, connect to the VPS remotely by the following command

iptables -A INPUT -p tcp -m tcp--dport 22 -j ACCEPT

Note: You can change the SSH configuration to a different port if needed      
     
If you hold a permanent IP address, you can allow connection to SSH and the connection is available only to users around your location.

Once after finding your IP address you can create the firewall rule to allow traffic to the SSH port and then replace YOUR_IP_ADDRESS with the actuall IP.

iptables -A INPUT -p tcp -s YOUR_IP_ADDRESS -m tcp --dport 22 -j ACCEPT

You can open more ports on your firewall by changing the port numbers, so that you can access the services you require. In order to use outgoing connections add the below rule

iptables -I INPUT -m state--state ESTABLISHED,RELATED -j ACCEPT

Through this you will receive replies from the VPS on the other side of the connection.Once set up is done you can block everything else, and allow all other outgoing connections.

iptables -P OUTPUT ACCEPT

iptables -P INPUT DROP

Save the configuration

Now list the rules to see if anything is missing out

iptables -L –n               

-n : indicates only ip addresses, not a domain name

You can save your firewall configuration by

iptables-save | sudo tee /etc/sysconfig/iptables

To ensure everything works fine, just restart the firewall. The saved rules will run even when the VPS is rebooted.

service iptables restart

Flush to unlock yourself

In-case if you block yourselves from accessing the VPS, the Digital Ocean web interface will allow us to connect to the server via console access.
To get back to the VPS again, you can use the follwing command which will flush the filters, once logged in.

iptables -F

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7 Tips to free disk space on cPanel server

When you run out of disk space, you might experience downtime, slow website loading, or emails that get sent but dose not arrive in your mailbox. You can follow below tips to free your disk sapce and maximize your server’s potential.

1.Delete user cPanel backups

Initially, You need to check whether the backup feature in cPanel is enabled or not. It will take plenty of your disk space usage, If you have got larger servers, as your users might have stored the backups on the server instead of downloading and removing them. By using the below command you can delete all user cPanel backups on the server.

for user in `/bin/ls -A /var/cpanel/users` ; do rm -fv /home/$user/backup-*$user.tar.gz ; done

Similarly, if you’re using the cPanel Backup System and are storing your backups locally on the server, you could be using twice as much space as you need to. Hence you can mount a backup server to your hosting server and store the backups there.

2. Delete cPanel File Manager temp files

You can remove the user uploaded files in File Manager within cPanel, as it creates a temp file that might not get removed upon upload.
rm -fv /home/*/tmp/Cpanel_*

3. Move or archive logs

Most of the server’s logs are stored in /var/log, which will populate your servers. Moreover, you can change the length of time and frequency of the log rotation in /etc/logrotate.conf and also enable compression to save additional space.

4. Remove cPanel update archives

You can delete or move /usr/local/apache.backup*
/home/cpeasyapache (actual name might vary based on cpanel version)
to a backup server to free little bit of space, as Cpanel and EasyApache updates leave behind files that are required.

5. Clean up Yum files

You can clean up all unwanted yum files by running a simple command, as yum updates leave package cache files on the server.
yum clean all

6. Remove pure-ftp partials

You need to find and delete your users uploaded files to the server via FTP when your server runs pure FTP as an FTP daemon. Next, the FTP server creates temporary files starting with .pureftpd-upload* that rename the actual filename when the upload is complete.
locate .pureftpd-upload | xargs rm –fv

7. Decrease the reserved disk space

You might have noticed that while checking the disk space. For example you might be using 900GB out of a 1TB drive, but it shows only 50GB available. This is because the other 50GB is reserved.
Such as for a large drives you really don’t need the whole 5%. Hence the best is to set this value to 2500 blocks and you can utilize more disk space. You can simply follow the below command.
tune2fs -r 2500 /dev/sda1


Note: You need to add the main command on the tune2fs command before you use it. This shows other options for setting the reserved space for your partitions.

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Setup YUM Repository on RHEL 8 using DVD

This guide will help you to set up a local yum repository to use locally-mounted DVD with Red Hat Enterprise Linux (RHEL) 8. This local repository lets you save internet bandwidth as well as the time for downloading packages from the internet. Since the packages are downloaded via a local network, the updates will happen at a lightning speed. YUM is a widely used software package management utility for RPM (RedHat Package Manager) based Linux systems, which makes software installation easy on Red Hat.
Repositories are generally stored on a public network, which can be accessed by multiple users on the internet. Red Hat Enterprise Linux 8 is split across two repositories,

•  BaseOS
• Application Stream (AppStream)

1. BaseOS – It provides the parts of the distribution that give you a running userspace on physical hardware, a virtual machine, a cloud instance or a container.
2. AppStream – It provides all the applications you might want to run in a given userspace.

Let's start : You need to mount the DVD ROM on any directory of your wish. For testing, we will
mount it on /soft.

Create a .repo file

Before creating a <name>.repo file, move the existing files present in
/etc/yum.repos.d/directory to/tmp, if no longer required.

mv /etc/yum.repos.d/*.repo /tmp/ 

Create a repo file called local.repo under /etc/yum.repos.d directory.

vi /etc/yum.repos.d/local.repo 

Base OS
[LocalRepo_BaseOS]
name=LocalRepository_BaseOS
baseurl=file:///soft/BaseOS
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
 

App Stream                                                                                                                       [LocalRepo_AppStream]
name=LocalRepository_AppStream
baseurl=file:///soft/AppStream
enabled=1
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release

Note : 
[LocalRepo] - Name of the Section
name - Name of the repository
baseurl - Location of the package
Enabled - Enable repository
gpgcheck - Enable secure installation (gpgcheck is optional (If you set gpgcheck=0, there is no need to mention gpgkey)
gpgkey - Location of the key

There you go, you have successfully configured the local yum repository. If you need any assistance Contact Us.

If this guide was helpful share it with your friends, as this may help someone who is looking for how to create one in RHEL 8.

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