Mail server

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Running an Email Server

  • Mail Transport/Transfer Agents (MTAs) - send messages between servers (required)
  • Mail Delivery Agents (MDAs) - store messages in the recipient's mailbox (required)
  • Mail User Agents (MUA) - software for reading messages

You need a domain name and appropriate MX records in your DNS.


  • Linux: Email Services
  • Linux System Engineer: Mail Systems Using Postfix
  • Linux Foundation Cert Prep: Email Services (Ubuntu)


SMTP (send)

SMTP (Simple Mail Transfer Protocol) .

There are several alternatives to SMTP (Simple Mail Transfer Protocol) servers for sending and receiving emails, each with its own advantages and use cases. Some of these alternatives include:

  • Third-Party Email APIs:
  • WebSockets:
  • Message Queues:
  • Peer-to-Peer (P2P) Protocols:
  • Custom Protocols: In some cases, organizations or projects may develop their custom communication protocols for specific use cases, which can be an alternative to SMTP.
  • Direct Socket Connections

Gmail is not an SMTP server; rather, it is an email service provided by Google that uses the SMTP protocol for sending and receiving emails. Gmail utilizes SMTP (Simple Mail Transfer Protocol) for outgoing email (sending) and other email retrieval protocols like IMAP and POP3 for incoming email (receiving).

When you send an email from your Gmail account, your email client or application communicates with Gmail's SMTP server to send the email. The SMTP server is responsible for delivering your email to the recipient's email server.

IMAP, POP3, Exchange (receive)

IMAP allows you to access your email wherever you are, from any device. When you read an email message using IMAP, you aren't actually downloading or storing it on your computer; instead, you're reading it from the email service. Changes made to emails (read/unread status, folders, etc.) are synchronized across devices because the emails remain on the server.

POP works by contacting your email service and downloading all of your new messages from it. Once they are downloaded onto your PC or Mac, they are deleted from the email service.

Exchange offers the same syncing capabilities as IMAP, plus much more. Exchange is a Microsoft product, giving you the ability to still use Outlook as your email service and benefit from Exchange functionality.


Introduction to Linux Postfix Architecture for Beginners

Configure Postfix to use Gmail as a Mail Relay

Adding Users, change user full name for Postfix


  1. Set Your Domain Name:
    myhostname =

    This parameter specifies the mail server's fully-qualified domain name.

  2. Set the Relayhost: If you want to relay outgoing emails through another SMTP server (common for sending emails to external domains), find the relayhost parameter and set it to the address of the SMTP server you want to relay through. You might also need to configure SMTP authentication for the relay host.
    relayhost = []:587
  3. Other Important Parameters: mydestination (list of domains that your server should consider local), mynetworks (IP addresses or networks allowed to relay through your server), and various security settings.
  4. sudo systemctl restart postfix

Setup a Local Only SMTP Email Server

# Send to another user in the same machine
echo "This is the email body" | sendmail -v -f sender_username receiver_username
sudo receiver_username

Send-only SMTP server

How to Build an Email Server on Ubuntu Linux


See Docker method


Raspberry Pi Email Server

Make Your Own Raspberry Pi Email Server

Ways to Keep Your Email Address Hidden

6 Ways to Keep Your Email Address Hidden


DuckDuckGo Can Now Block Your Emails From Being Tracked

Send from google emails on Ubuntu

Change your google account to use less secure authentication. Otherwise it won't work and you will receive an email with a subject "Critical security alert" after you try to send out an email.

sudo apt install mailutils
sudo nano /etc/postfix/   # no account information
sudo nano /etc/postfix/sasl_passwd # contains account information
cat /etc/ssl/certs/thawte_Primary_Root_CA.pem | sudo tee -a /etc/postfix/cacert.pem
sudo chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
sudo chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
sudo apt-get install --reinstall postfix
sudo /etc/init.d/postfix restart
sudo /etc/init.d/postfix reload
echo "Test Email message body" | mail -s "Email test subject" [email protected] # works

We can actually send to other email accounts. For example, we can use mailR package to send emails in R

send.mail(from = "[email protected]",
  to = c("[email protected]"),
  replyTo = c("[email protected]"),
  subject = "Test",
  body = "test",
  smtp = list( = "", port = 465, 
     = "yourname", passwd = "XX", ssl = TRUE),
  authenticate = TRUE,
  send = TRUE)

New domain

If you just bought a new domain name do not forget to fix it's emails!

Use Zoho Mail With Your Domain

How to Migrate from Gmail to Zoho Mail With Your Domain

How to Send an Email with a Different “From” Address in Outlook

How to Send an Email with a Different “From” Address in Outlook. How Email Providers Handle Messages Sent From a Different “From” Address? How Do Scammers Use Fake “From” Addresses?

Bash Script to Send a Mail When ...

Bash Script to Send a Mail About New User Account Creation


Install WebMail Lite PHP based Webmail Client on Debian 9.1

You have new mail

What is the "You have new mail" message in Linux/UNIX?

Command line tools

6 Ways to Send Email from the Linux Command Line:

  • mail
  • mailx
  • mutt
  • mpack
  • sendmail
  • ssmtp

mail command

  • Mailutils includes programs for reading, composing, and sending email, as well as managing mailboxes and user accounts. Mailutils can be used with a variety of mail servers, including Postfix, Exim, Sendmail, and Courier.
  • We still need to install Postfix in order to send emails. Postfix is an open-source mail transfer agent (MTA) that routes and delivers email to accounts that are external to the system. When you install Mailutils on Ubuntu, it will also install Postfix as a dependency if you don't already have some other MTA installed. See How To Install and Configure Postfix as a Send-Only SMTP Server on Ubuntu 20.04.
  • Use dpkg -l | grep postfix to check if postfix is installed.
  • To reconfigure postfix, use sudo dpkg-reconfigure postfix
  • How to Use the Linux mail Command
  • Send Email in Linux from Command Line.
    • While the command line emails clients are a lot simpler and less computationally intensive, you can only use them to send email to personal email domains and not to Gmail or Yahoo domains because of extra authentication required. Also, you cannot receive emails from external SMTP servers. Generally, it’s a lot easier if you use GUI email clients like Thunderbird or Evolution to avoid undelivered emails problem.
  • Details
    sudo apt install mailutils postfix
    # Tab. OK
    # Default is "Internet Site". OK
    # Enter 'System mail name'
    #   If I enter, emails (to: [email protected]) can be sent externally 
    #   If I enter, emails will be sent internally on the local host
    #   The value will be saved in /etc/postfix/
    • Configure postfix: sudo nano /etc/postfix/
    • Scroll to the bottom and change "inet_interfaces = all" to "inet_interfaces = loopback-only"
      • The reason emails were sent internally or externally is b/c the setting of System mail name. This will be written to the mydestination in /etc/postfix/ Emails sent do anything in mydestination will be delivered locally. So in my case, I need to put instead of in the "System mail name" (not the same as the screen explanation).
    • systemctl restart postfix
    • echo "This is the body" | mail -s "This is the subject" -a "FROM:[email protected]" [dest address]
    • Not work. Check /var/log/mail.log file (I'm using Debian 11). It shows the mails were delivered to the local user. ls /var/mail/$USER. Or switch to the user and run "mail".
    • It works if I limit the dest address to use my domain name instead of host.domain-name. Not understand if it is b/c I use
  • The mydestination parameter in the file of your Postfix configuration specifies a list of domains for which your mail server will accept mail as the final destination. This parameter helps Postfix determine whether it should deliver incoming email locally or relay it to another mail server.
    • Local Delivery: When an email is addressed to a domain listed in the mydestination parameter, Postfix will consider that domain as a local destination. This means that Postfix will attempt to deliver the email to a mailbox or user on the local server. For example, if your mydestination parameter includes, and an email is sent to [email protected], Postfix will deliver the email locally.
    • Relaying: If a domain is not listed in mydestination, Postfix will treat it as a non-local destination and may relay the email to another mail server based on its routing and transport configurations. This is typically used when your mail server acts as a relay host for domains it doesn't host locally.
    • Wildcards: You can use wildcard characters in mydestination to match multiple subdomains or domains. For example, to include all subdomains of, you can use *
    For example, mydestination = $myhostname, localhost.$mydomain,, *
    • $myhostname refers to the fully-qualified domain name (FQDN) of your mail server.
    • localhost.$mydomain specifies that the server should accept mail for the local hostname (e.g.,
    • is an explicit domain for which your server will accept mail.
    • * is a wildcard entry that matches all subdomains of


Mutt is a command line email app for Linux and here's how to set it up

sendemail package

sendEmail -f $USERNAME -s \
            -xu $USERNAME -xp $PASSWORD -t $USERNAME \
            -o tls=yes \
            -u "Web page changed" \
            -m "Visit it at $URL"

sendEmail -f [email protected] -t [email protected] \
            -s -xu [email protected] -xp YOURPASSWORD \
            -o tls=yes \
            -u "Hello from sendEmail" \
            -m "How are you? I'm testing sendEmail from the command line."


How to Set Up a Mail Server with Modoboa on Debian 10


Install and Configure Kolab Groupware on Ubuntu 16.04 LTS

Criptext: private email service


How to Install Zimbra Collaboration Suite 8.8 on Ubuntu

Temporary/Disposable email

Create A Temporary Email From The Command Line With tmpmail

Trouble shooting