How to Create an Email Server with Mail-in-a-Box

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If you chose to host your own email server, but after reading through Running a Mail Server you got discouraged by the complexity of this process, then there’s another solution: Mail-in-a-Box. The name is fitting since the software manages to pack everything you need from a mail server, in one single allegorical box. It includes:

  • Postfix, as the Simple Mail Transfer Protocol (SMTP) server.
  • Dovecot, as the Internet Message Access Protocol (IMAP) server; it’s what allows you to sync mail with your phone, read/send messages, delete them, etc.
  • CardDAV/CalDAV implemented through Nextcloud (a fork of OwnCloud that includes more features); this enables you to sync your address book and calendar events.
  • Z-push to implement the Exchange ActiveSync protocol so that mail can be “pushed” to your phone as soon as it arrives on the server.
  • Roundcube webmail, which helps you manage your email by using a web browser.
  • Nsd4 Domain Name System (DNS) server; this saves you the hassle of manually adding DNS entries to configure Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting and Conformance (DMARC), features used to battle spam on the Internet; properly configured, these increase the likelihood that your server will be seen as “legit” by other servers
  • A backup service
  • A control panel, also accessible through the web browser, that:
    • Greets you with a comprehensive system status check that makes you aware of any possible problems with your server and offers advice on how to fix them;
    • Lets you add or remove mailboxes, change passwords, backup data, change DNS settings;
    • Does a great job at explaining what each setting does and how it should be used. It also includes examples on how to interact with its Application Programming Interface (API) so that you can automate tasks, such as creating a mailbox through your own application/website (e.g., user registers on your website to get an email account)
  • If you’re interested in the details, you can read about the components here: Mail-in-a-Box Components

The preconfigured box of software is also fairly security-conscious and you can read more about it here: Security features enabled in Mail-in-a-Box

This guide may involve or result in sending email. In an effort to fight spam, Linode restricts outbound connections on ports 25, 465, and 587 on all Linodes for new accounts created after November 5th, 2019. For more information, please see Sending Email on Linode.
This guide may involve or result in sending email. In an effort to fight spam, Linode restricts …

Before You Begin

  1. Make sure your domain name registrar allows you to use custom nameservers and set glue records.

  2. Follow our Setting Up and Securing a Compute Instance guide to update your system, create a limited user account, and harden SSH access. Do not yet configure a fiewall or fail2ban as that might clash with what Mail-in-a-Box will set up (e.g., it implements its own fail2ban rules).

If you insist on using a password for root instead of a private key, at least use a very good password. Bots constantly scan the Internet for SSH servers and try random passwords. Some are more aggressive than others, and while fail2ban helps block IPs, there’s always the next bot (with a different IP) that will visit and have another try. Keep in mind that strings such as h4x0r123, while they may look strong because they mix letters and numbers, are actually very weak.

Wherever you see in this tutorial, replace it with your domain name, and leave the prefix as it is. That is, don’t change box to something else. Also, is used as an example IP; your outputs should reflect your server IP instead.

Launch Ubuntu 18.04 Server

Use this server exclusively for Mail-in-a-Box. Installing extra software might cause unexpected behavior.

Choose a server with at least 1GB of RAM. If you plan to host many users (mailboxes) and/or expect a high volume of email traffic, you can start out with 2GB or more. Don’t forget to boot the server.

Make sure you select Ubuntu 18.04 as the Operating System (OS), as starting with version 0.40 only Ubuntu 18.04 is supported.

Configure Your Domain Name

You’ll have to check with your registrar, the company where you’ve registered your domain name with, to see how you can change your nameservers and add glue records. Either search for this information on Google, the site’s knowledge base, or ask their support to help you.

Here’s what you’ll need to do:

  1. Log in to your account on your domain name registrar’s site. Find the page where you can enter your nameservers, and add these values:
  2. Now, find the page where you can set up glue records. Then, add these entries, replacing with the IP address of your server:

You might have noticed you’re using the same IP in both entries. There are a few registrars that have a problem with this, so you may not be able to save these settings and will have to contact their support team. Alternatively, you can skip using your box as a DNS host, and keep your registrar’s DNS host. You will find all the needed records in the System -> External DNS tab of the administration console, once you’ve completed installation.

Also note that some registrars may only require you to enter as they autocomplete the rest of your hostname, Carefully examine the page to see which variant you should use.

  1. This shouldn’t suffer the delays of DNS propagation (since it’s a nameserver change, not a DNS record change), but you can still check if everything is correct and proper with:

     dig NS +trace

You should see your nameservers at the end of the output:

;; Received 595 bytes from in 343 ms		300	IN	NS		300	IN	NS
dig: couldn't get address for '': no more

At this point you can continue. If you don’t see the required data, then come back later and check again. If after one hour it’s still missing, then contact your registrar’s support team.

Install Mail-in-a-Box

This guide is written for a non-root user. Commands that require elevated privileges are prefixed with sudo. If you’re not familiar with the sudo command, see the Users and Groups guide.
  1. After you log in to your server with an SSH client, update all the software packages on your server:

     sudo apt-get update && sudo apt-get upgrade

If you notice a reboot is needed (usually when the Linux kernel is upgraded), type sudo reboot at the command prompt to restart your server.

  1. If you’re able to understand bash scripts, at least vaguely, and you want to see what the following step will execute on your server, you can check this link in your browser and have a read: Mail-in-a-Box Bash Script .

  2. To start the install process, run the following command:

     curl -s | sudo bash

It will start to download software and after a while greet you with a Text User Interface (TUI), which is a way to present a more user-friendly install wizard under the limitations of a terminal. You can navigate the menus with the arrow keys and simply press ENTER to make the desired selections.

Every step is thoroughly explained in the terminal output.

Install Wizard Steps

  1. When you’re prompted to choose an email address, delete the pre-filled value and replace it with You can replace your_name with whatever you desire, as long as it’s a valid username.

  2. In the next step, the hostname should look like this:

    Now, the install wizard should continue to download and configure software packages. Just wait for it to do its magic.

  3. At the next step, you’ll be prompted to choose your timezone. Use the arrow keys to make the desired selection and press ENTER.

    Once again, Mail-in-a-Box will continue to pull in required packages and auto-configure them. Wait for it to finish, it will take longer this time.

  4. When it finishes installing the packages, the script will prompt you to choose a password for the administrative account. Choose a good password since this is the most powerful account that can make any change in the control panel. This will also be the password to the email account you set up in Step 1.

  5. When package auto-configuration is complete, you’ll be prompted to install a Transport Layer Security (TLS) certificate. If Let’s Encrypt cannot verify that you own your domain (i.e., DNS changes haven’t yet propagated to its servers), then this step will be automatically skipped, but you can still request your certificate later from the control panel of Mail-in-a-Box.

  6. At this point the script has finished its job and you’ll be prompted with this message in the terminal output:

    Your Mail-in-a-Box is running.
    Please log in to the control panel for further instructions at:
    You will be alerted that the website has an invalid certificate. Check that
    the certificate fingerprint matches:

In the unlikely event that DNS changes have propagated fast enough to Linode’s resolvers, the output will be slightly different:

Your Mail-in-a-Box is running.

Please log in to the control panel for further instructions at:

If you have a DNS problem put the box's IP address in the URL
( but then check the TLS fingerprint: D2:69:5E:47:52:E6:3D:48:FB:23:80:F4:E7:8B:22:D4:94:71:91:91:C9:89:15:65:85:99:90:94:97:24:F6:8D

Now, you can access the control panel in your web browser. After logging in, you’ll be greeted with a page showing you status checks for all the moving parts of your mail server. This page is incredibly useful, centralizing all the information you need to see to make sure everything is working correctly. It also describes how you can resolve possible problems.

Install TLS Certificate and Add PTR Record

Since it’s very likely that a Let’s Encrypt TLS certificate hasn’t been installed yet, let’s do that now.

  1. Type this command in the server to check if Linode received your DNS changes:


    When you see your server IP in the A record, you can continue; otherwise try again later.

    ;; ANSWER SECTION:		1724	IN	A
  2. In the top-left menu you’ll notice an element called System. Click on it and then select TLS (SSL) Certificates. Now click on the blue button that says Provision and within a few minutes the certificate status should change to Signed & valid.

  3. Follow this guide, How to Configure Reverse DNS on a Linode Server , to set up a pointer record (PTR). Make sure you set it to This step is very important to execute and pass some antispam checks. Without it, a lot of mail servers will flag your outbound email as spam and will consider it suspicious that your IP doesn’t point to your domain name, and sometimes even reject it.


As you can see, it’s very convenient when everything for an email server is packaged in one place and automatically configured. But convenience often has a price. Mail-in-a-box’s centralization - that makes it easy to manage everything - also creates a single point of failure. There is a safety net though: email servers are intelligent enough to retry sending you their data for a few days, in case your server is unavailable.

If you can’t afford the delay, you should look at ways to make your setup more reliable. A beginner friendly approach is to set up a monitoring system that will notify you quickly in case of problems. Later on, you can look into secondary (slave) nameservers, secondary MX entries, cloning and syncing Mail-in-a-Box machines, and floating IPs.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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