How to Quickly Set Up a Mail Server on CentOS 7 with Modoboa

Setting up a mail server on Linux from scratch is a pain in the neck. This tutorial is going to show you how to quickly set up your own email server on CentOS 7 with Modoboa, saving you lots of time and headaches. Modoboa is a free and open source mail hosting and management platform designed to work with Postfix SMTP server and Dovecot IMAP/POP3 server.

Modoboa is written in Python, released under the terms of ISC license. At the time of writing, the latest version is v1.14.0, released on July 5, 2019. Main features of Modoboa are as follows:

  • Modoboa by default uses Nginx web server to serve the webmail client and web-based admin panel.
  • Compatible with Postfix and Dovecot.
  • Supports MySQL/MariaDB, and PostgreSQL database.
  • Easily create unlimited mailboxes and unlimited mail domains in a web-based admin panel.
  • Easily create email alias in the web-based admin panel.
  • The webmail client provides an easy-to-use message filter to help you organize messages to different folders.
  • It can help you protect your domain reputation by monitoring email blacklists and generating DMARC report, so your emails have better chance to land in inbox instead of spam folder.
  • Includes amavis frontend to block spam and detect virus in email.
  • Calendar and address book.
  • Integration with Let’s Encrypt to get valid SSL/TLS certificate.
  • Includes AutoMX to allow end users to easily configure mail account in a desktop or mobile mail client.

Step 1: Choose the Right Hosting Provider and Buy a Domain Name

To set up a complete email server with Modoboa, you need a server with at least 2GB RAM, because after the installation, your server will use more than 1GB of RAM. This tutorial is done on a $10/month Vultr VPS (virtual private server). I recommend Vultr because it allows you to send emails via port 25, so you can send unlimited emails (transactional email and newsletters) without spending money on SMTP relay.

Other VPS providers like DigitalOcean blocks port 25. DigitalOcean would not unblock port 25, so you will need to set up SMTP relay to bypass blocking, which can cost you additional money.

Create an account at Vultr, then create a server instance in the Vultr web control panel and install CentOS 7 on it. There are 4 types of server in Vultr. Here we will choose the $10/month plan in Cloud Compute, which costs less than the other 3 types and is good enough to run Modoboa.

vultr mail server

It is recommended that you follow the instructions below on a clean install of CentOS 7.

You also need a domain name. I registered my domain name from NameCheap because the price is low and they give whois privacy protection free for life.

Also, make sure your server IP address isn’t listed in any email blacklist. You can go to mxtoolbox.com and dnsbl.info to check your server IP address. If it’s in a blacklist, you can delete your server instance in Vultr and create a new one. As Vultr uses an hourly billing model, you won’t be charged by month, but by how many hours you used, which makes it convenient to delete a server instance at any time.

Step 2: Creating MX Record and A Record in DNS

The MX record specifies which host or hosts handle emails for a particular domain name. For example, the host that handles emails for linuxbabe.com is mail.linuxbabe.com. If someone with a Gmail account sends an email to [email protected], then Gmail server will query the MX record of linuxbabe.com. When it finds out that mail.linuxbabe.com is responsible for accepting email, it then query the A record of mail.linuxbabe.com to get the IP address, thus the email can be delivered.

You can log in to your domain registrar’s website (such as NameCheap) to create DNS records.

In your DNS manager, create a MX record for your domain name. Enter @ in the Name field to represent the main domain name, then enter mail.your-domain.com in the Value field.

modoboa web interface

Note: The hostname for MX record can not be an alias to another name. Also, It’s highly recommended that you use hostnames, rather than bare IP addresses for MX record.

Your DNS manager may require you to enter a preference value (aka priority value). It can be any number between 0 and 65,356. A small number has higher priority than a big number. You can enter 0 for your email server, or accept the default value.

After creating MX record, you also need to create an A record for mail.your-domain.com , so that it can be resolved to an IP address. If your server has IPv6 address, be sure to add AAAA record as well.

If you use Cloudflare DNS service, you should not enable the CDN feature when creating A record for your mail server. Cloudflare does not support SMTP proxy.

Step 3: Set up Mail Server on CentOS 7 with Modoboa Installer

Log into your server via SSH, then run the following command to update existing software packages.

sudo yum update

Download modoboa installer from Github.

sudo yum install git

git clone https://github.com/modoboa/modoboa-installer

Modoboa is written in Python. Run the following command to install the necessary Python software.

sudo yum install python-virtualenv python-pip

Then navigate to the modoboa-installer directory and create a configuration file. Replace example.com with your own domain name.

cd modoboa-installer

sudo ./run.py --stop-after-configfile-check example.com

modoboa-mail-server-centos-7

Edit the configuration file installer.cfg with a command line text editor like nano.

sudo nano installer.cfg

To obtain a valid SSL/TLS certificate from Let’s Encrypt for your mail server, in [certificate] section, change the value of type from self-signed to letsencrypt.

type = letsencrypt

And change the email address from [email protected] to your real email address, which will be used for account recovery and important notifications.

modoboa installer

By default, Modoboa installer will install PostgreSQL database server, as indicated by the following lines in the config file.

[database]
engine = postgres
host = 127.0.0.1
install = true

If you would like to use MariaDB database server, then change the engine from postgres to mysql.  (Modoboa will install MariaDB instead of MySQL.)

modoboa mariadb database

To save the file in Nano text editor, press Ctrl+O, then press Enter to confirm. Press Ctrl+X to exit. Next, run the following command to open port 80 and 443 in firewall, so we can access the web-based admin panel later.

sudo firewall-cmd --permanent --zone=public --add-service=http
sudo firewall-cmd --permanent --zone=public --add-service=https

Reload firewall for the changes to take effect.

sudo systemctl reload firewalld

Now run the following command to start the installation.

sudo ./run.py --interactive example.com

install-modoboa-centos-7

The installation process can take a while. It took 10 minutes on my Vultr server. If you see an error during the installation, you can use the --debug option to see more detailed output.

sudo ./run.py --interactive --debug example.com

After Modoboa finishes installation, you can log into the admin panel with username admin and password password.

modoboa-mail-server-debian 9

Once you are logged in, you should go to Admin -> Settings -> Profile to change the password.

modoboa install

Step 4: Adding Mailboxes in Modoboa Admin Panel

Please note that the default admin account isn’t an email account. It can only be used to administer the mail server. To send emails, you need to add mailboxes with the admin account.

Go to Domains tab and click Add button to add a new domain.

modoboa review

Then enter your main domain name in the Name field. It is highly recommended that you enable DKIM signing, which can help with your domain reputation. In Key selector filed, you can enter a random word like modoboa.  Choose 2048 for the key length.

adding domain name in modoboa

In the next screen, you can choose to create an admin account for this particular domain name. The SMTP protocol requires that a mail server should have a [email protected] address.

modoboa postmaster account

Click the Submit button and your domain name will be added in Modoboa.

To add email addresses, go to Domains tab and click your domain name.

add mailboxes in modoboa

Then click mailboxes.

adding email addresses in modoboa

Click Add button and choose Account.

modoboa alias

Then choose Simple user as the role. Enter an email address in Username field and enter a password.

qucikly set up an email server modoboa

In the next screen, you can optionally create an alias for this email address.

create alias in modoboa

After clicking the submit button, the email address is created.

Step 5: Sending Test Emails

Before sending test emails, we need run the following commands to open the SMTP and IMAP related ports in the firewall.

sudo firewall-cmd --permanent --add-service=smtp
sudo firewall-cmd --permanent --add-service=smtp-submission
sudo firewall-cmd --permanent --add-service=smtps
sudo firewall-cmd --permanent --add-service=imap
sudo firewall-cmd --permanent --add-service=imaps

Reload firewall for the changes to take effect.

sudo systemctl reload firewalld

To login to the Modoboa webmail, you need to log out the admin account first and then enter the credentials for the email address.

modoboa login

Once you are logged into Modoboa webmail, you can send a test email from your private email server to your other email address and vice versa.

modoboa webmail

Inbound emails will be delayed for a few minutes, because by default Modoboa enables greylisting, which tells other sending SMTP server to try again in a few minutes. This is useful to block spam. The following message in /var/log/maillog indicates greylisting is enabled.

postfix/postscreen[20995]: NOQUEUE: reject: RCPT from [34.209.113.130]:36980: 450 4.3.2 Service currently unavailable;

Step 6: Unblocking Port 25 for Your Vultr Server

Your ISP or hosting provider won’t block incoming connection to port 25 of your server, which means you can receive emails from other mail servers.  However, many ISP/hosting providers block outgoing connection to port 25 of other mail servers, which means you can’t send emails.

If your emails didn’t arrive at your other email address such as Gmail, you should check the mail log (/var/log/maillog). The following message in /var/log/maillog indicates port 25 is blocked.

mail postfix/smtp[9969]: connect to gmail-smtp-in.l.google.com[74.125.200.27]:25: Connection timed out
mail postfix/smtp[9969]: connect to gmail-smtp-in.l.google.com[2404:6800:4003:c03::1b]:25: Connection timed out

If port 25 is blocked for outgoing connections on your Vultr server, then you should open a support ticket in your Vultr account. They will unblock port 25 for you. Here’s what I said to the support stuff.

Hi

I'm setting up a mail server. Looks like port 25 is blocked on this server. Please open it for me.

Thanks :)

The support stuff replied very quickly:

Hello XIAO GUOAN,

Thank you for your SMTP unblock request!

In order to combat spam and spam-like activities, we will need to review some additional information prior to removing the SMTP filter.

Please reply to this ticket with the following information:

1. The business name and organization URL(s) under which you offer services.
2. Describe, in as much detail as possible, the nature of the emails you intend to send.
3. The volume of email that you plan to deliver on a daily/monthly basis.

We need to know this in order to make an informed decision regarding your account settings and resource limits to ensure the integrity of our network/systems/online reputation.

Customer Support
www.Vultr.com

So you just need to answer 3 simple questions. You can use the following as a template.

Hi

My business name is LinuxBabe and website is https://www.linuxbabe.com,

I'm setting up this mail server for my website, so I would be able to send registration emails and notification emails to my users.

The volume of outgoing email is below 100 emails per day.

Thanks.

And then the stuff replied:

Hello,

Thank you for the information provided!

We have removed the default SMTP block on your account. Please restart any active instances via https://my.Vultr.com for the change to take effect (restarting via the server itself _will_not_ work).

Also, keep in mind that marketing and bulk email is restricted in our platform. For reference, our ANTI-SPAM policy is listed here: https://www.Vultr.com/legal/antispam_policy.php

If you have any additional questions our team is happy to assist you further. Thank you for choosing Vultr!

Kind Regards,
Customer Support

Once they removed the SMTP block on your account, you need to restart your server via the Vultr control panel for the change to take effect. Note that you can use Vultr server so send newsletters, as long as the recipients subscribed for it, but you are not allowed to send spam.

If your ISP or hosting provider (such as DigitalOcean) refuses to unblock port 25, then you can’t send emails directly, you also need to set up SMTP relay to solver this problem.

Step 7: Using Mail Clients on Your Computer or Mobile Device

Fire up your desktop email client such as Mozilla Thunderbird and add a mail account.

  • In the incoming server section, select IMAP protocol, enter mail.your-domain.com as the server name, choose port 143 and STARTTLS. Choose normal password as the authentication method.
  • In the outgoing section, select SMTP protocol, enter mail.your-domain.com as the server name, choose port 587 and STARTTLS. Choose normal password as the authentication method.

modoboa-mail-server-desktop-mail-client-configuration-automx

You can also use IMAP on port 993 with SSL/TLS encryption.

Step 8: Improving Email Deliverability

To prevent your emails from being flagged as spam, you should set PTR, SPF, DKIM and DMARC records.

PTR record

A pointer record, or PTR record, maps an IP address to a FQDN (fully qualified domain name). It’s the counterpart to the A record and is used for reverse DNS lookup, which can help with blocking spammers. Many SMTP servers reject emails if no PTR record is found for the sending server.

To check the PTR record for an IP address, run this command:

dig -x IP-address +short

or

host IP-address

Because you get IP address from your hosting provider or ISP, not from your domain registrar, so you must set PTR record for your IP in the control panel of your hosting provider or ask your ISP.  Its value should be your mail server’s hostname: mail.your-domain.com. If your server uses IPv6 address, be sure to add a PTR record for your IPv6 address as well.

To edit the reverse DNS record for your Vultr server, log into Vultr control panel, select your server and the Settings tab. Then you can edit the reverse DNS record for both IPv4 and IPv6 address.

modoboa mail server PTR record

SPF Record

SPF (Sender Policy Framework) record specifies which hosts or IP address are allowed to send emails on behalf of a domain. You should allow only your own email server or your ISP’s server to send emails for your domain. In your DNS management interface, create a new TXT record like below.

modoboa spf record

Explanation:

  • TXT indicates this is a TXT record.
  • Enter @ in the name field to represent the main domain name.
  • v=spf1 indicates this is a SPF record and the version is SPF1.
  • mx means all hosts listed in the MX records are allowed to send emails for your domain and all other hosts are disallowed.
  • ~all indicates that emails from your domain should only come from hosts specified in the SPF record. Emails that are from other hosts will be flagged as forged.

To check if your SPF record is propagated to the public Internet, you can use the dig utility on your Linux machine like below:

dig your-domain.com txt

The txt option tells dig that we only want to query TXT records.

DKIM Record

DKIM (DomainKeys Identified Mail) uses a private key to digitally sign emails sent from your domain. Receiving SMTP servers verify the signature by using the public key, which is published in the DNS DKIM record.

When we were adding domain name in Moboboa admin panel earlier, we enabled DKIM signing, so the signing part is taken care of. The only thing left to do is creating DKIM record in DNS manager. First go to Modoboa admin panel as the admin user and select your domain name. In the DNS section, click Show key button.

modoboa dkim signing

The public key will be revealed. There are two formats. We only need the Bind/named format.

modoboa dkim public key

Go to your DNS manager, create a TXT record, enter modoboa._domainkey in the Name field. (Recall that we used modoboa as the selector when adding domain name in the admin panel.) Copy everything in the parentheses and paste into the value field. Delete all double quotes. Your DNS manager may require you to delete other invalid characters, such as carriage return.

modoboa dkim format

For those who are interested, Modoboa uses OpenDKIM to generate private key for your domainkey and verify signatures of inbound emails.

DMARC Record

DMARC stands for Domain-based Message Authentication, Reporting and Conformance. DMARC can help receiving email servers to identify legitimate emails and prevent your domain name from being used by email spoofing.

To create a DMARC record, go to your DNS manager and add a TXT record. In the name field, enter _dmarc. In the value field, enter the following:

v=DMARC1; p=none; pct=100; rua=mailto:[email protected]

create dmarc record txt

The above DMARC record is a safe starting point. To see the full explanation of DMARC, please check the following article.

Step 9: Testing Email Score and Placement

After creating PTR, SPF, DKIM record, go to https://www.mail-tester.com. You will see a unique email address. Send an email from your domain to this address and then check your score. As you can see, I got a perfect score.

imporve email server reputation

Mail-tester.com can only show you a sender score. There’s another service called GlockApps that allow you to check if your email is placed in the recipient’s inbox or spam folder, or rejected outright. It supports many popular email providers like Gmail, Outlook, Hotmail, YahooMail, iCloud mail, etc

glockapps email placement test

Auto-Renew Let’s Encrypt TLS Certificate

Modoboa installed the latest version of Let’s Encrypt client (certbot) as /opt/certbot-auto. Let’s Encrypt TLS certificate is valid for 90 days. To automatically renew the certificate, edit root user’s crontab file.

sudo crontab -e

Add the following line at the end of this file.

@daily /opt/certbot-auto renew -q && systemctl reload nginx postfix dovecot

Save and close the file. This tells Cron to run the certbot renew command every day. If the certificate has 30 days left, certbot will renew it. It’s necessary to reload Nginx web server, Postfix SMTP server and Dovecot IMAP server so they can pick up the new certificate.

Enabling SMTPS Port 465

If you are going to use Microsoft Outlook client, then you need to enable SMTPS port 465 in Postfix SMTP server.

(Optional) Set Up Autodiscover and AutoConfig to Automate Mail Client Configuration

Autodiscover and AutoConfig make it easy to configure a desktop or mobile mail client. The end user just need to enter a name, email address and password to set up his/her mail account, without having to enter the SMTP or IMAP server details. Autodiscover is supported by Microsoft Outlook mail client and AutoConfig is supported by Mozilla Thunderbird mail client.

Modoboa uses AutoMX to implement this feature on your mail server. All we need to do now is add CNAME records in DNS. In your DNS manager, create two CNAME records.

autoconfig.yourdomain.com       CNAME         mail.yourdomain.com
autodiscover.yourdomain.com     CNAME         mail.yourdomain.com

Go to the Domains tab in your Modoboa admin panel, if the autoconfig is in green, that means your CNAME records are correct. (Modoboa checks DNS records for your mail server every 30 minutes, so you might need to wait some time for autoconfig to turn green.)

modoboa automx

Once the CNAME records are propagated to Internet, you don’t have to enter the SMTP or IMAP server details when setting up mail account in Microsoft Outlook and Mozilla Thunderbird.

Host Multiple Domains in Modoboa

See the following article:

Wrapping Up

I hope this tutorial helped you set up a mail server on CentOS 7 with Modoboa. As always, if you found this post useful, then subscribe to our free newsletter to get more tips and tricks. Take care 🙂

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2 Responses to “How to Quickly Set Up a Mail Server on CentOS 7 with Modoboa

  • vanhussen
    4 days ago

    In your opinion, which email server is better for my ubuntu server. Is it Modoboa, iRedMail, Postfix, or Mailtrain?

    • Modoboa and iRedMail are scripts that make it easy to install and configure various components of a mail server. Personally, I prefer Modoboa, because it allows you to easily create alias in the web-based admin panel.

      Postfix is a just a SMTP server.

      Mailtrain is a newsletter application.

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