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hatem ben tayeb
hatem ben tayeb

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Mailcow: Setting up a full featured self hosted mail server

#docker #selfhosted #mailcow #email

Setting up a full featured mail server is an actual PAIN for a system admin, you have to interconnect many software pieces and a lot of testing espacially security and spam if you plan to use it for your company ... In this Post i will take you in my journey of setting up a full featured mail server, i was searching a lot on the internet and i didn't get a sweetable answer to move on .. but finally i successfully made it ! .. It works with multiple domains, secure and no spam problems !

For the reader

I assume you have knowledge about how email works, Mail DNS records, linux, docker and SSL of course. This guide is not for beginners

If you dont have enough knowledge, take a seat and take a look here :

Term Definition
Mail server Is a computer system that sends and receives email source
MX
CNAME Used to alias one name to another,CNAME stands for Canonical Name. source
DKIM Is an email authentication technique that allows the receiver to check that an email was indeed sent and authorized by the owner of that domain source
SPF Is an email-authentication technique which is used to prevent spammers from sending messages on behalf of your domain source
DMARC is an email validation system designed to protect your company’s email domain from being used for email spoofing source

Mailcow

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Mailcow is a free, open source software project. A Mailcow server is a collection of Docker containers running different mail server applications, SOGo, Postfix, Dovecot etc. Mailcow provides a modern and easy to use web interface to create and manage email accounts. You can visit the official documentation

I ill not make a comparison about different opensource self hosted mail servers, rather then that i will give you a great repo that includes owesome softwares marked as self hosted, you can check the Email section come here

If you want some thoughts about mailcow from real users check this reddit discussions : come here and here

Server Requirements

The recommended OS to run mailcow is ubuntu 18.04, also don't use cento7 packages on cento8 because the maintainers said :

Do not use CentOS 8 with Centos 7 Docker packages. You may create an open relay.

For the resources i bought a VPS from OVH cloud provider with :

  • 2 VCPU
  • 4 GB of RAM
  • 80 GB storage

Docker installed : 



curl -sSL https://get.docker.com/ | CHANNEL=stable sh
systemctl enable docker.service
systemctl start docker.service
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Docker-compose installed : 



curl -L https://github.com/docker/compose/releases/download/$(curl -Ls https://www.servercow.de/docker-compose/latest.php)/docker-compose-$(uname -s)-$(uname -m) > /usr/local/bin/docker-compose
chmod +x /usr/local/bin/docker-compose
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If you have a firewall, you should allow those ports : 



netstat -tulpn | grep -E -w '25|80|110|143|443|465|587|993|995|4190'
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Note : you must have a clean server means no other applications or a reverse proxy becaue mailcow has every thing in place.

Okay now every thing is good ! but there is another thing to verify which is our IP !!!
we have to test it if it is blacklisted, if yes it's a huge problem ... we can't proceed anymore because your mails will not be delivered, it's all about your host reputation!.

We can check it with an online service called mxtoolbox by visiting this url mxtoolbox.

Basic DNS configuration

Before we proceed we have to get a domain name from any provider, i got one from OVH, and i delegated to AZURE DNS SERVICE, it dosen't matter actually, we will have the same configuration in any provider.

I pretend that i have :

  • Root Domain name : mymailserver.com
  • Server IP address : 1.2.3.4

Let's get started !

Create an A record

In your provider DNS pannel add an A record like this

  • Name : mail
  • Type : A
  • TTL : default
  • Value : 1.2.3.4

You can confirm with the dig command : 



 dig mail.mymailserver.com +noall +answer
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Create the CNAME records

In your provider DNS pannel add a CNAME record for the autoconfig like this

  • Name : autoconfig
  • Type : CNAME
  • TTL : default
  • Alias : mail.mymailserver.com

Test it with : dig autoconfig.mymailserver.com +noall +answer

Add another CNAME record for the autodiscover like this :

  • Name : autodiscover
  • Type : CNAME
  • TTL : default
  • Alias : mail.mymailserver.com

Test it with : dig autodiscover.mymailserver.com +noall +answer

Create the an MX record

In your root domain add an MX domain to point to your mail server domain :

  • Name : @/empty
  • Type : MX
  • TTL : default
  • Prefenerence/periorty : 10 or 0
  • Mail Exchange : mail.mymailserver.com

rDNS configuration

Get more information about rDNS here

You can configure your rDNS on the provider of your server and change the generated domain name to your mail domain mail.mymailserver.com

and test it with dig -x 1.2.3.4 +noall +answer, should get mail.mymailserver.com as responce.

Security DNS Records

Authenticate your mail server and protect it from Fake identities and Domain spoofing attacks we have to setup those records

SPF record

In your root domain add a TXT record like this :

  • Name : @/empty
  • Type : TXT
  • TTL : default
  • value : v=spf1 ip4:1.2.3.4 -all

Test it with dig mymailserver.com TXT

DKIM record

Setting up the dkim record needs a public key to be inserted in the record here but we can't now because we have to install mailcow and get the public key given by our mail server, we will leave it empty for now.

  • Name : dkim._domainkey
  • Type : TXT
  • TTL : default
  • value : v=DKIM1;k=rsa;t=s;s=email;p=

DMARC record

The best thing you can do for dmarc is to make a free account on dmarcian, it will give you a record like this : 



v=DMARC1; p=reject; rua=mailto:<dmarc email1>; ruf=<dmarc email2>
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Just add it to your domain DNS pannel like this :

  • Name : _dmarc
  • TTL : default
  • value : v=DMARC1; p=reject; rua=mailto: dmarc email1 ; ruf=dmarc email2

Test is with : dig _dmarc.mymailserver.com TXT

That's it for the DNS configurations, all records are in place execpt the dkim value we ill add it later

Install mailcow

You need git installed to clone the repo in your server : 



 git clone https://github.com/mailcow/mailcow-dockerized
 cd mailcow-dockerized
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Your in the repo now, so run the script ./generate_config.sh
 to generate your config, for the hostname add mail.mymailserver.com, it will request a certificate from Let'svEncrypt automatically.

To run your mail server just use this command : 



docker-compose pull
docker-compose up -d
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You need to wait some time to download all the containers, run them and provision a SSL certificate.

The default credentials to access are admin & moohoo (you must change it with your own)

Verify that all containers are healthy with the green icon like this :

Screenshot_2021-01-08 mailcow UI.png

Well done ! Let's proceed to add domains and mailboxes

Configure Mailcow

Our mail server is working now but there is neither domains or mailboxs configured. in this section we will go step by step .. let's GO !

Add your domain

Login to your mailcow admin panel :

  1. Select configuration on the top bar then select mail setup
  2. Click on add domain then add your root domain mymailserver.com and click on Add domain and restart SoGo
  3. Select configuration again then click on configuration & details
  4. In the hosizontal menu click configuration and click on ARC/DKIM keys
  5. Scroll to bottom and fill the domain/s form with your domain mymailserver.com
  6. On the selector type dkim
  7. Select 2048 on the DKIM key length and click add
  8. Copy the generated public key that starts with v=DKIM1;k=rsa;t=s;s=email;p= ...
  9. Go to your DNS pannel and modify the TXT record with the generated value
  10. Wait until your DNS modification propagate

You can validate your configuration for SPF, DKIM and DMARC with this site, you should get result like this (don't forget to put dkim as a selector` :

Screenshot_2021-01-08 Free DMARC Domain Check Is Your Domain Protected - dmarcian.png

Create a Mailbox for mymailserver.com

By default mailcow give 10GB of storage to every domain and every mailbox under that domain has 3GB of storage .. so feel free to modify them to your needs,

To create a mailbox folow those steps :

  1. Under configuration on the to bar click mail setup and select mailboxes`
  2. Click add mailbox
  3. Choose a username , your domain (it will be loaded automatically) and then add a password and click add
  4. On the top bar click apps and then webmail, you will be redirected to the SoGo UI , login wiyh your newly created mail and password
  5. on the bottom click on the green icon, you will get an interface of sending a mail
  6. In your browser open another tab and go to this site : mail-tester.com and copy the mail address.
  7. Return to your SoGo interface and send a mail with that mail, on the body make sure to add some text with a least two paragraphs.
  8. Wait 10 seconds and go the mail-tester.com and click on then check your score

And BOOM you should get this result You Can Send :

Screenshot_2021-01-07 Spam Test Result.png

Feel free to send a mail to your friends and your own Gmail address, don't worry Gmail still don't know your mail server, so he will placed as spam, just unspam it !, try to send it to zoho mail for example. The test again with other tools i suggest to use :

  • Mxtoolbox SuperTool and select test mail server
  • Dkimvalidator and send an email to the given address, make sure that all tests are oassed like the dmarcian.com tests.

Add another domain to mailcow

I assume we have a second domain : myseconddomain.com.
I will not repeat the same steps it's quite easy so let's go :

  1. Create A record : mail.myseconddomain.com that points to your Host 1.2.3.4
  2. Create a CNAME record : autoconfig that points to mail.myseconddomain.com
  3. Create a CNAME record : autodiscover that points to mail.myseconddomain.com
  4. Create an MX record: on the root domain add 10 as periority and mail.myseconddomain.com as target
  5. Create SPF record like we did earlier
  6. Create DMARC record as we did earlier
  7. Create DKIM record and in the same time add your new domain as we did earlier and copy the generated DKIM key to your DKIM record.
  8. Validate your records
  9. Add a mailbox under your new domain and send an email to mail-tester.com and dkimvalidator.com, you should get 10/10 sweetheart :)

Final thoughts

Don't send a lot of mails directly you will be blocked ! ... so start step by step by sending 20 mails per day for the first week then try sending 80 the next week ... after 2 months you can send a lot of mails like 1000 mails, but take in mind that you need to add the list unsubscribe headers to your postfix to allow users to unsubscribe against your newsletters/subscriptions.

please follow me on twitter @hatem ben tayeb

Top comments (5)

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jiapei100 profile image
JIA Pei •

There is ONLY i issue leftover, please refer to github.com/mailcow/mailcow-dockeri... . The current FULL featured solution does NOT provide multiple respective SSLs . I mean: it looks mail.myseconddomain.com and mail.mymailserver.com are sharing the same SSL at /var/lib/acme/mail.mymailserver.com/cert.pem . When setting up tools like Thunderbird, Outlook, etc., I actually met github.com/mailcow/mailcow-dockeri... . Is it possible to have such outcome:

  • 1 single mail server
  • multiple domains: mail.domain1.com, mail.domain2.com, mail.domain3.com, etc.
  • multiple respective SSL corresponds to respective domain?

Cheers

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crossrt profile image
Rui Tai Low •

Hi, thank you for writing this post. It's very helpful for me!
But I have a question:
according to your setup, the server IP has only 1 PTR record (rDNS).
if that case, emails sent by myseconddomain.com might failed because some email services will reject the email due to wrong/missing PTR record right?

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chownroot profile image
chown-root •

The best thing to do is for the 2nd domain to point its mx record to the same A record as the 1st domains mx record so that both domains work with the same single PTR record.
So, in step 4 of "Add another domain to mailcow " the mx record must point to the A record as 1st domains mx record.
Hope this makes sense?

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rich1488 profile image
rich • • Edited

curl -L https://github.com/docker/compose/releases/download/$(curl -Ls https://www.servercow.de/docker-compose/latest.php)/docker-compose-$(uname -s)-$(uname -m) > /usr/local/bin/docker-compose

gets this

bash: /usr/local/bin/docker-compose: Permission denied

EDIT: Solved, I think.

But now when pulling docker compose pull
I get this;
no matching manifest for linux/arm/v7 in the manifest list entries

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daniel15 profile image
Daniel Lo Nigro •

In addition to the A record, you should also add an AAAA record for IPv6 connectivity :)