Given the long history of email (dating back to 1971), and the massive number of email servers online, you’d be right to assume that there are many different email server platforms available. However, according to the securityspace.com survey, three types of email servers account for more than 95% of the global market share:<\/p>\n
- \n
- \n
- \n
- Exim<\/li>\n
- Postfix<\/li>\n
- Sendmail<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n
The top three email servers on the internet are Exim (with over 55%), Postfix (over 30%), and Sendmail (about 4%). All three of these email platforms, and Qmail, were originally developed for Unix-Like or Linux based Operating Systems.<\/p>\n
Today, with the widespread availability of easy and low-cost cloud-hosted server providers, anyone can setup their own email server. This guide focuses on deploying, configuring, and discussing best practices and security concerns for Exim, Postfix, Sendmail, and Qmail.<\/p>\n
<\/p>\n
Exim – Overview + Pros & Cons<\/b><\/h3>\n
Exim is an MTA (Mail Transfer Agent) for Unix-like operating systems first written in 1995 by Philip Hazel. Exim is licensed under the GPLv2 license. Exim is used extensively all around the world. According to the study noted earlier\u00a0 (http:\/\/www.securityspace.com\/s_survey\/data\/man.201907\/mxsurvey.html<\/a>), as of 2019 Exim accounted for approximately 57% of all online public email servers on the internet. Exim4 is currently the default MTA on all Debian-based GNU\/Linux systems, including Ubuntu.<\/p>\n
Exim – Pros<\/b><\/span><\/h4>\n
- \n
- Default MTA on Debian-based Linux distributions<\/li>\n
- Easy install, basic install is guided via user interface<\/li>\n
- Popular and well documented<\/li>\n
- Plenty of community support<\/li>\n
- Secure<\/li>\n<\/ul>\n
Exim – Cons<\/b><\/span><\/h4>\n
- \n
- Arguably more difficult to maintain\/administer post-deployment than Postfix<\/li>\n<\/ul>\n
<\/p>\n
Postfix – Overview + Pros & Cons<\/b><\/h3>\n
Postfix is an MTA (mail transfer agent) for Unix-like operating systems developed by Wietse Venema in partnership with IBM in 1997. Postfix is licensed under the IBM Public License. As of 2019, Postfix is still under active development by its creator and a team of contributors. According to the following study (http:\/\/www.securityspace.com\/s_survey\/data\/man.201907\/mxsurvey.html<\/a>),as of 2019 Postfix accounted for approximately 34% of all online public email servers on the internet.<\/p>\n
Postfix – Pros<\/b><\/span><\/h4>\n
- \n
- Easy to configure and use<\/li>\n
- Elegant (author\u2019s opinion)<\/li>\n
- Popular and well documented<\/li>\n
- Plenty of community support<\/li>\n
- Secure<\/li>\n<\/ul>\n
Postfix – Cons<\/b><\/span><\/h4>\n
- \n
- No Windows port<\/li>\n<\/ul>\n
<\/p>\n
Sendmail – Overview + Pros & Cons<\/b><\/h3>\n
Sendmail is an MTA (mail transfer agent) for Unix-like operating systems first released in 1983. Sendmail is a descendant of the original ARPANET delivermail program written by Eric Allman. Allman developed Sendmail as a replacement for delivermail for BSD systems, starting with BSD version 4.1c in 1983. Sendmail is licensed under the Sendmail license. At one point (1996), Sendmail accounted for approximately 80% of all public email servers available on the internet. According to the Security Space study (http:\/\/www.securityspace.com\/s_survey\/data\/man.201907\/mxsurvey.html<\/a>), in 2019 Sendmail accounted for approximately 4% of all online public email servers on the internet. Sendmail was acquired by Proofpoint in 2013.<\/p>\n
Sendmail – Pros<\/b><\/span><\/h4>\n
- \n
- Native Windows port available<\/li>\n<\/ul>\n
Sendmail – Cons<\/b><\/span><\/h4>\n
- \n
- Not as easy to configure as Exim or Postfix<\/li>\n
- Not as efficient with resources<\/li>\n<\/ul>\n
<\/p>\n
Qmail – Overview + Pros & Cons<\/b><\/h3>\n
Qmail is an MTA (mail transfer agent) for Unix-like operating systems first developed in 1995 by Daniel J. Bernstein. At its release, Qmail was touted as a more secure replacement for Sendmail. Qmail\u2019s source code was released to the public domain by its author. According to the Security Space study (http:\/\/www.securityspace.com\/s_survey\/data\/man.201907\/mxsurvey.html<\/a>), in 2019 Qmail accounted for approximately 0.07% of all online public email servers on the internet.<\/p>\n
Qmail – Pros<\/b><\/span><\/h4>\n
- \n
- Secure<\/li>\n
- Low resource requirements<\/li>\n<\/ul>\n
Qmail – Cons<\/b><\/span><\/h4>\n
- \n
- Unmaintained<\/li>\n
- Most complicated of the four to install<\/li>\n
- Config file structure and general operation is less elegant than Postfix or Exim<\/li>\n
- Not as popular as the others (less than 1% market share)<\/li>\n
- No Windows port<\/li>\n<\/ul>\n
<\/p>\n
Installation and Configuration Procedure – Environment Setup Notes<\/b><\/h3>\n
Unless otherwise specified, the following environment is used for all installation and configuration procedures to follow:<\/p>\n
- \n
- Ubuntu Server 18.04.3 LTS\n
- \n
- Kernel Version: 4.15.0-1045-aws<\/li>\n<\/ul>\n<\/li>\n
- Running on an entry-level Amazon Lightsail instance (at the time of this writing, $3.50\/mo)\n
- \n
- 512 MB RAM<\/li>\n
- 1 vCPU<\/li>\n
- 20GB SSD<\/li>\n
- 1 TB Bandwidth<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
These procedures assume you are starting with a fresh installation of Ubuntu.<\/p>\n
As always, don\u2019t forget to start by fully updating Ubuntu:<\/strong><\/p>\n
sudo apt-get update && sudo apt-get dist-upgrade<\/code><\/p>\nAlso, we will need to allow TCP port 25 (the default SMTP port) through the firewall. In our Amazon Lightsail environment, that looks like this:<\/p>\n
![\"lightsail1\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/lightsail1.png\")
<\/a><\/p>\n<\/p>\n
How to Use Mutt Email Client to Send a Test Email<\/b><\/h3>\n
Mutt is a lightweight, CLI-only email client. It is very useful for testing and as a lightweight general purpose email client.<\/p>\n
To install Mutt:<\/p>\n
sudo apt-get install mutt<\/code><\/p>\n![\"mutt1\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/mutt1.png\")
<\/a><\/p>\nWe\u2019re not going to go into a full configuration of Mutt. To manually launch Mutt and tell it to use our Maildir, run this:<\/p>\n
mutt -f ~\/Maildir<\/code><\/p>\nMutt will ask you if you want to create \/home\/ubuntu\/Mail (we don\u2019t) so just press n<\/p>\n
Once Mutt starts, it will look like this:<\/p>\n
![\"mutt2\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/mutt2.png\")
<\/a><\/p>\nTo send a test email with Mutt, do the following:<\/p>\n
- \n
- To start the mail, press m<\/li>\n
- Enter the email address to which you want to send a test email<\/li>\n
- Enter the subject of the test email<\/li>\n
- You will then enter Nano text editor to write the body of your message. Write whatever you want.<\/li>\n
- When finished writing your test message, press ctrl + x<\/li>\n
- Then press y<\/li>\n
- Then press enter<\/li>\n<\/ol>\n
If it has been done correctly, you should see something like this:<\/p>\n
![\"mutt3\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/mutt3.png\")
<\/a><\/p>\nFinally, press y to send the email, and you should see \u201cmail sent.\u201d<\/p>\n
Now, let\u2019s go check our email to see if the message was delivered. Since this is a brand new email server with no DNS configuration or SPF, DKIM or DMARC, our test message will most likely be flagged as spam (if it gets delivered at all). For our tests, we used a Gmail account, and we were able to find our message in the spam folder:<\/p>\n
![\"mutt4\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/mutt4.png\")
<\/a><\/p>\nOur email was delivered! This means our email server is correctly sending outbound mail.<\/p>\n
<\/p>\n
Basic Install & Config Procedure for Exim<\/b><\/h3>\n
Exim – Intro & Unique Considerations<\/b><\/span><\/h4>\n
Exim version 4 is the default MTA for Debian-based Linux distributions, including Ubuntu 18. Therefore, installing Exim4 on Ubuntu is very straightforward.<\/p>\n
Exim – Common config files<\/b><\/span><\/h4>\n
\/etc\/exim4\/update-exim4.conf.conf – This is the config file where all settings configured via the configuration user interface are stored. You can either edit this file directly, or re-run
sudo dpkg-reconfigure exim4-config<\/code><\/p>\n\/var\/lib\/exim4\/config.autogenerated – This is the master configuration file that is generated automatically every time you run
sudo update-exim4.conf<\/code><\/p>\nThis file should NOT be edited manually.<\/p>\n
Exim – Useful commands<\/b><\/span><\/h4>\n
To start the Exim4 daemon:<\/p>\n
sudo systemctl start exim4.service<\/code><\/p>\nTo stop the Exim4 daemon:<\/p>\n
sudo systemctl stop exim4.service<\/code><\/p>\nTo restart the Exim4 daemon:<\/p>\n
sudo systemctl restart exim4.service<\/code><\/p>\nTo generate main Exim4 config files:<\/p>\n
sudo update-exim4.conf<\/code><\/p>\nRun the configuration user interface for Exim4:<\/p>\n
sudo dpkg-reconfigure exim4-config<\/code><\/p>\nExim – Procedure<\/b><\/span><\/h4>\n
First, see what Exim4 package is available in the default repositories:<\/p>\n
sudo apt-cache policy exim4<\/code><\/p>\n(At the time of this writing, Exim version 4.90-1 is available in the default repositories.)<\/p>\n
![\"exim1\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim1.png\")
<\/a><\/p>\nTo install Exim4, run the following:<\/p>\n
sudo apt-get install exim4<\/code><\/p>\n![\"exim2\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim2.png\")
<\/a><\/p>\nTo configure Exim4, run the following, which will display a user interface for configuring many Exim parameters:<\/p>\n
sudo dpkg-reconfigure exim4-config<\/code><\/p>\nYou should see the following screen, allowing you to choose the type of mail server configuration you want. For this example, we will be configuring Exim as an \u201cinternet site\u201d or an email server that sends and receives email directly over the internet via SMTP.<\/p>\n
![\"exim3\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim3.png\")
<\/a><\/p>\nThe next screen will prompt you to enter the \u201cmail name\u201d of the server. This should be the domain name where you want to receive email. We will use the name \u201csjno.net.\u201d<\/p>\n
![\"exim4\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim4.png\")
<\/a><\/p>\nThe next screen asks us to define on which IP addresses we want to listen for incoming SMTP connections. Since we want this server to be publicly available to the internet, we will set this to blank.<\/p>\n
![\"exim5\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim5.png\")
<\/a><\/p>\nThe next screen asks us to define our \u201clocal domains.\u201d Local domains are domains for which this email server should be considered the final destination. We will use the domain \u201csjno.net.\u201d<\/p>\n
![\"exim6\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim6.png\")
<\/a><\/p>\nThe next screen asks us to define our \u201crelay domains.\u201d Relay domains are non-local domains. In our case, this is everything other than \u201csjno.net.\u201dFor now, we will leave this as the default value (blank).<\/p>\n
![\"exim7\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim7.png\")
<\/a><\/p>\nThe next screen asks us to define IP addresses for which this system will unconditionally relay email messages. This is useful if we are setting up this email server to be a dedicated \u201cMail Relay\u201d or \u201cSmarthost.\u201d For now, we will leave this as the default value (blank).<\/p>\n
![\"exim8\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim8.png\")
<\/a><\/p>\nThe next screen configures DNS lookup settings. For now, we will leave this as the default value (No).<\/p>\n
![\"exim9\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim9.png\")
<\/a><\/p>\nThe next screen asks us our preference between two common local mail formats. These two formats are called \u201cmbox\u201d and \u201cmaildir.\u201d This choice is mostly user preference. We prefer Maildir, so that is what we will select here.<\/p>\n
![\"exim10\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim10.png\")
<\/a><\/p>\nThe next screen asks us whether or not we want to split Exim4\u2019s configuration into smaller files, as opposed to the default \u201cmonolithic\u201d configuration. There are pros and cons to each. For this example, we are going to choose not to split the config files (No).<\/p>\n
![\"exim11\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim11.png\")
<\/a><\/p>\nThe next screen asks us where mail addressed to postmaster@ and root@ should be delivered. If we leave this blank, mail for those recipients will be saved in \/var\/mail\/mail (not recommended). We will enter the username of our default user, which is \u201cubuntu.\u201d<\/p>\n
![\"exim12\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim12.png\")
<\/a><\/p>\nExim – Testing Initial Installation<\/b><\/span><\/h4>\n
We now have a basic installation of Exim! Let\u2019s make sure it started and is running OK.<\/p>\n
Run this:<\/p>\n
ps aux | grep exim4<\/code><\/p>\nIf Exim is running, the above command should output something similar to this (we can see that there is a running process \/usr\/sbin\/exim4):<\/p>\n
![\"exim13\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim13.png\")
<\/a><\/p>\nNext, run this:<\/p>\n
sudo service exim4 status<\/code><\/p>\nIf Exim was started successfully, the command above should output something similar to this (we can see that the active status shows \u201cactive (running)\u201d ):<\/p>\n
![\"exim14\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim14.png\")
<\/a><\/p>\nNext, run this:<\/p>\n
netstat -aln | grep 25<\/code><\/p>\nWe should see that our server is listening on port 25:<\/p>\n
![\"exim15\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim15.png\")
<\/a><\/p>\nAlso, we should now be able to use a free web-based tool to verify that our server is up and listening to the world. We like to use the \u201cTest Email Server\u201d tool from mxtoolbox.com\u2019s SuperTool (https:\/\/mxtoolbox.com\/SuperTool.aspx#<\/a>).<\/p>\n
If we point the \u201cTest Email Server\u201d test to the public IP address of our Amazon Lightsail instance, we should see something like this:<\/p>\n
![\"exim16\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/exim16.png\")
<\/a><\/p>\nTo send a test email using the Mutt email client, refer to the section: How to Use Mutt Email Client to Send a Test Email<\/b><\/p>\n
These tests prove that our basic Exim email server is up, listening, and can send mail. You may be thinking \u201cbut that\u2019s just an IP Address! What about DNS?\u201d Continue on to the DNS Setup for Mail Server<\/b> section for steps on configuring the basic DNS-related settings.<\/p>\n
Exim – Troubleshooting<\/b><\/span><\/h4>\n
Server doesn\u2019t appear to be listening or responding from the outside?<\/p>\n
Don\u2019t forget to open port 25 on your firewall. (See instructions for AWS in the environment notes section.)<\/p>\n
<\/p>\n
Basic Install & Config Procedure for Postfix<\/b><\/h3>\n
Postfix – Intro \/ Unique Considerations<\/b><\/span><\/h4>\n
Postfix is available in the default Ubuntu repositories, therefore installing Postfix is rather straightforward.<\/p>\n
Postfix – Common config files<\/b><\/span><\/h4>\n
\/etc\/aliases<\/p>\n
\/etc\/postfix\/main.cf<\/p>\n
\/etc\/postfix\/master.cf<\/p>\n
Postfix – Useful commands<\/b><\/span><\/h4>\n
To start Postfix:<\/p>\n
sudo postfix start<\/code><\/p>\nTo stop Postfix:<\/p>\n
sudo postfix stop<\/code><\/p>\nTo restart Postfix:<\/p>\n
sudo postfix restart<\/code><\/p>\nAfter modifying main.cf, be sure to run:<\/p>\n
service postfix reload<\/code><\/p>\nTo modify Postfix config programmatically:<\/p>\n
sudo postconf<\/code><\/p>\nTo see how to use Postconf:<\/p>\n
man postconf<\/code><\/p>\nPostfix – Procedure<\/b><\/span><\/h4>\n
First, let\u2019s see what Postfix package is available in the default repositories:<\/p>\n
sudo apt-cache policy postfix<\/code><\/p>\n(At the time of this writing, Postfix version 3.3.0 is available in the default repositories.)<\/p>\n
![\"postfix1\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix1.png\")
<\/a><\/p>\nTo install Postfix, run the following:<\/p>\n
sudo apt-get install postfix<\/code><\/p>\n![\"postfix2\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix2.png\")
<\/a><\/p>\nYou should immediately be greeted by Postfix\u2019s configuration user interface.<\/p>\n
You should see the following screen, allowing you to choose the type of mail server configuration you want. For this example, we will be configuring Postfix as an \u201cinternet site\u201d or an email server that sends and receives email directly over the internet via SMTP.<\/p>\n
![\"postfix3\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix3.png\")
<\/a><\/p>\nThe next screen will prompt you to enter the \u201cmail name\u201d of the server. This should be the domain name where you want to receive email. We will use the name \u201csjno.net.\u201d<\/p>\n
![\"postfix4\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix4.png\")
<\/a><\/p>\nImmediately after hitting enter on this screen, the Postfix configuration user interface will close and Postfix will start scrolling through some automated configuration and startup output. Be sure to read this output for useful tips on performing additional Postfix configuration.<\/p>\n
By default, Postfix uses Mbox mail format. We prefer Maildir. First, let\u2019s manually create the Maildir directory structure for our Ubuntu user:<\/p>\n
mkdir -p \/home\/ubuntu\/Maildir\/{cur,new,tmp}<\/code><\/p>\nThen configure Postfix to use Maildir:<\/p>\n
sudo postconf -e mailbox_command=<\/code><\/p>\nsudo postconf -e home_mailbox=Maildir\/<\/code><\/p>\nThen, tell Postfix to reload its config:<\/p>\n
sudo postfix reload<\/code><\/p>\nPostfix – Testing Initial Installation<\/b><\/span><\/h4>\n
We now have a basic installation of Postfix! Let\u2019s make sure it started and is running OK.<\/p>\n
ps aux | grep postfix<\/code><\/p>\nIf Postfix is running, the above command should output something similar to this (we can see that there are several Postfix processes running):<\/p>\n
![\"postfix5\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix5.png\")
<\/a><\/p>\nsudo service postfix status<\/code><\/p>\nIf Postfix started successfully, the command above should output something similar to this (we can see that the active status shows \u201cactive (exited)\u201d):<\/p>\n
![\"postfix6\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix6-150x146.png\")
<\/a><\/p>\nnetstat -aln | grep 25<\/code><\/p>\nYou should see that your server is listening on port 25:<\/p>\n
![\"postfix7\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix7.png\")
<\/a><\/p>\nAlso, Postfix has its own status command:<\/p>\n
sudo postfix status<\/code><\/p>\n![\"postfix8\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix8-300x19.png\")
<\/p>\nWe should now also be able to use a free web-based tool to verify that our server is up and listening to the world. We like to use the \u201cTest Email Server\u201d tool from mxtoolbox.com\u2019s SuperTool (https:\/\/mxtoolbox.com\/SuperTool.aspx#).<\/p>\n
If we point the \u201cTest Email Server\u201d tool to the public IP address of our Amazon Lightsail instance, we should see something like this:<\/p>\n
![\"postfix9\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/postfix9.png\")
<\/a><\/p>\nTo send a test email using the Mutt email client, refer to the section How to Use Mutt Email Client to Send a Test Email<\/b><\/p>\n
These tests prove that our basic Postfix email server is up, listening, and can send mail! You may be thinking \u201cbut that\u2019s just an IP Address. What about DNS?” Continue on to the DNS Setup for Mail Server<\/b> section for steps on configuring the basic DNS-related settings.<\/p>\n
Postfix – Troubleshooting<\/b><\/span><\/h4>\n
Server doesn\u2019t appear to be listening or responding from the outside?<\/p>\n
Don\u2019t forget to open port 25 on your firewall. (See instructions for AWS in the environment notes section.)<\/p>\n
<\/p>\n
Basic Install & Config Procedure for Sendmail<\/b><\/h3>\n
Sendmail – Intro \/ Unique Considerations<\/b><\/span><\/h4>\n
Sendmail is available in the default Ubuntu repositories, therefore installing Sendmail is fairly straightforward, though not as simple as Exim or Postfix.<\/p>\n
Sendmail – Common config files<\/b><\/span><\/h4>\n
\/etc\/aliases<\/p>\n
\/etc\/hosts<\/p>\n
\/etc\/mail\/sendmail.mc<\/p>\n
Sendmail – Useful commands<\/b><\/span><\/h4>\n
To start Sendmail:<\/p>\n
sudo service sendmail start<\/code><\/p>\nTo stop Sendmail:<\/p>\n
sudo service sendmail stop<\/code><\/p>\nTo restart Sendmail:<\/p>\n
sudo service sendmail restart<\/code><\/p>\nTo run the Sendmail setup user interface:<\/p>\n
sudo sendmailconfig<\/code><\/p>\nRun this command whenever you update the \/etc\/aliases file:<\/p>\n
sudo newaliases<\/code><\/p>\nSendmail – Procedure<\/b><\/span><\/h4>\n
First, let\u2019s see what Sendmail package is available in the default repositories:<\/p>\n
sudo apt-cache policy sendmail<\/code><\/p>\n(At the time of this writing, Sendmail version 8.15.2 is available in the default repositories.)<\/p>\n
![\"sendmail1\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/sendmail1.png\")
<\/a><\/p>\nTo install Sendmail, run the following:<\/p>\n
sudo apt-get install sendmail<\/code><\/p>\n
- Ubuntu Server 18.04.3 LTS\n
- Native Windows port available<\/li>\n<\/ul>\n
- No Windows port<\/li>\n<\/ul>\n
- Arguably more difficult to maintain\/administer post-deployment than Postfix<\/li>\n<\/ul>\n
![\"sendmail2\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/sendmail2.png\")
<\/a><\/p>\n![\"sendmail3\"](\"https:\/\/www.gmass.co\/blog\/wp-content\/uploads\/2019\/09\/sendmail3.png\")
<\/a><\/p>\n