Difference between revisions of "Sendmail"

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[[Category:Mail Server]]
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[[Category:Mail server]]
Sendmail is the classical SMTP server from the unix world. It was originally coded long time ago, when the internet was a safer place, and back then, security didn't matter as much as does today. Therefore it used to have several security bugs and it got some bad reputation for that. But those bugs are long fixed and a recent sendmail version is as safe as any other SMTP server. If your top priority is security, you should probably use netqmail, however.
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[[ja:Sendmail]]
 +
[[zh-CN:Sendmail]]
 +
Sendmail is the classic SMTP server from the unix world. Arch Linux provides the alternative [[Postfix]] in the [[official repositories]].
  
The goal of this article is to setup Sendmail for local users accounts, '''without using mysql or other database''', and allowing also the creation of ''mail-only accounts''.  
+
The goal of this article is to setup Sendmail for local users accounts, '''without using mysql or other database''', and allowing also the creation of ''mail-only accounts''.
  
 
This article only explains the required steps configuring Sendmail; after that, you probably want to add IMAP and POP3 access, so you could follow the [[Dovecot]] article.
 
This article only explains the required steps configuring Sendmail; after that, you probably want to add IMAP and POP3 access, so you could follow the [[Dovecot]] article.
  
 
==Installation==
 
==Installation==
Install the package {{AUR|sendmail}} from the [[AUR]], and the packages {{Pkg|procmail}} and {{Pkg|m4}} from the [[Official Repositories|official repositories]].
+
[[Install]] the {{AUR|sendmail}}, {{Pkg|procmail}} and {{Pkg|m4}} packages.
 +
 
 
==DNS Records==
 
==DNS Records==
 
You should have a domain, and edit your MX records to point your server. Remember some servers have problems with MX records pointing to CNAMEs, so your MX should point to an A record instead.
 
You should have a domain, and edit your MX records to point your server. Remember some servers have problems with MX records pointing to CNAMEs, so your MX should point to an A record instead.
 +
 
==Adding users==
 
==Adding users==
* By default, all the local users can have an email address like username@your-domain.com. But if you want to add ''mail-only accounts'', that is, users who can get email, but can't have shell access or login on X, you can add them like this:
+
Create a [[Users and groups|Linux user]] for each user that wants to receive email at ''username@your-domain.com''. To add ''mail-only accounts'', that is, users who can get email, but can't have shell access or login on X, you can add them like this:
{{bc|useradd -m -s /sbin/nologin joenobody}}
+
# useradd -m -s /usr/bin/nologin ''username''
* Assign a password:
+
 
{{bc|passwd joenobody}}
+
 
==Configuration==
 
==Configuration==
 +
=== Create SSL certs ===
 +
 +
{{Warning|If you plan on implementing SSL/TLS, know that some variations and implementations are [https://weakdh.org/#affected still] [[wikipedia:Transport_Layer_Security#Attacks_against_TLS.2FSSL|vulnerable to attack]]. For details on these current vulnerabilities within SSL/TLS and how to apply appropriate changes to Sendmail, visit http://disablessl3.com/ and https://weakdh.org/sysadmin.html}}
 +
 +
Generate a key and obtain a certificate. See [[OpenSSL#Self-signed certificate]] for private use or [[Let's Encrypt]] for a free publicly-trusted certificate.
 +
 
===sendmail.cf===
 
===sendmail.cf===
* Create the file {{ic|/etc/mail/sendmail.mc}} with the following content:
+
Create the file {{ic|/etc/mail/sendmail.mc}}.
{{bc|
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You can read all the options for configuring sendmail on the file {{ic|/usr/share/sendmail-cf/README}}.
 +
 
 +
{{Warning|If you create your own sendmail.mc file, remember that plaintext auth over '''non-TLS''' is very risky. Using the following example forces TLS and is therefore more safe unless you know what are you doing}}
 +
 
 +
Here is an example using auth over [[Wikipedia:Transport_Layer_Security|TLS]]. The example has comments explaing how it works. The comments start with {{ic|dnl }}.
 +
 
 +
{{hc|/etc/mail/sendmail.mc|<nowiki>
 
include(`/usr/share/sendmail-cf/m4/cf.m4')
 
include(`/usr/share/sendmail-cf/m4/cf.m4')
 +
define(`confDOMAIN_NAME', `your-domain.com')dnl
 
FEATURE(use_cw_file)
 
FEATURE(use_cw_file)
dnl FEATURE(`relay_entire_domain')dnl
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dnl The following allows relaying if the user authenticates,
FEATURE(`access_db')dnl
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dnl  and disallows plaintext authentication (PLAIN/LOGIN) on
 +
dnl  non-TLS links:
 +
define(`confAUTH_OPTIONS', `A p y')dnl
 +
dnl
 +
dnl  Accept PLAIN and LOGIN authentications:
 +
TRUST_AUTH_MECH(`LOGIN PLAIN')dnl
 +
define(`confAUTH_MECHANISMS', `LOGIN PLAIN')dnl
 +
dnl
 +
dnl Make sure this paths correctly point to your SSL cert files:
 +
define(`confCACERT_PATH',`/etc/ssl/certs')
 +
define(`confCACERT',`/etc/ssl/cacert.pem')
 +
define(`confSERVER_CERT',`/etc/ssl/certs/server.crt')
 +
define(`confSERVER_KEY',`/etc/ssl/private/server.key')
 +
dnl
 
FEATURE(`virtusertable', `hash /etc/mail/virtusertable.db')dnl
 
FEATURE(`virtusertable', `hash /etc/mail/virtusertable.db')dnl
 
OSTYPE(linux)dnl
 
OSTYPE(linux)dnl
 
MAILER(local)dnl
 
MAILER(local)dnl
 
MAILER(smtp)dnl
 
MAILER(smtp)dnl
}}
+
</nowiki>}}
* Then process it with
+
 
{{bc|m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf}}
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Then process it with
 +
# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
  
 
===local-host-names===
 
===local-host-names===
* Create the file {{ic|/etc/mail/local-host-names}} and put there your domains:
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Put your domains on the {{ic|local-host-names}} file:
{{bc|
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{{hc|/etc/mail/local-host-names|
 
localhost
 
localhost
 
your-domain.com
 
your-domain.com
Line 39: Line 69:
 
localhost.localdomain
 
localhost.localdomain
 
}}
 
}}
 +
 +
Make sure the domains are also resolved by your {{ic|/etc/hosts}} file.
 +
 
===access.db===
 
===access.db===
* Create the file {{ic|/etc/mail/access}}  and put there the base addresses where you want to be able to relay mail. Lets supose you have a vpn on 10.5.0.0/24, and you want to relay mails from any ip in that range:
+
Create the file {{ic|/etc/mail/access}}  and put there the base addresses where you want to be able to relay mail. Lets suppose you have a vpn on {{ic|10.5.0.0/24}}, and you want to relay mails from any ip in that range:
{{bc|
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{{hc|/etc/mail/access|
 
10.5.0 RELAY
 
10.5.0 RELAY
 
127.0.0 RELAY
 
127.0.0 RELAY
 
}}
 
}}
* Then process it with
+
 
{{bc| makemap hash /etc/mail/access.db < /etc/mail/access}}
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Then process it with
 +
# makemap hash /etc/mail/access.db < /etc/mail/access
  
 
===aliases.db===
 
===aliases.db===
* Edit the file {{ic|/etc/mail/aliases}}  and  uncomment the line {{ic|#root:        human being here}} and change it to be like this:
+
Edit the file {{ic|/etc/mail/aliases}}  and  uncomment the line {{ic|#root:        human being here}} and change it to be like this:
 
{{bc|root:        your-username}}
 
{{bc|root:        your-username}}
* You can add aliases for your usernames there, like:
+
 
 +
You can add aliases for your usernames there, like:
 
{{bc|coolguy:      your-username
 
{{bc|coolguy:      your-username
 
somedude:    your-username}}
 
somedude:    your-username}}
* Then process it with
 
{{bc|newaliases}}
 
===virtusertable.db===
 
* Create the file {{ic|/etc/mail/virtusertable}}  and put there aliases that includes domains (useful if your server is hosting several domains)
 
  
{{bc|
+
Then process it with
 +
# newaliases
 +
 
 +
===virtusertable.db===
 +
Create your {{ic|virtusertable}} file and put there aliases that includes domains (useful if your server is hosting several domains)
 +
{{hc|/etc/mail/virtusertable|
 
your-username@your-domain.com        your-username
 
your-username@your-domain.com        your-username
 
joe@my-other.tk                      joenobody
 
joe@my-other.tk                      joenobody
 
}}
 
}}
* To forward all mail addressed to any user in the "my-other.tk" domain to "your-username@your-domain.com":
+
 
 +
Then process it with
 +
# makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable
 +
 
 +
=== Start on boot ===
 +
Enable and start the following services. Read [[Daemons]] for more datails.
 +
* {{ic|saslauthd.service}}
 +
* {{ic|sendmail.service}}
 +
* {{ic|sm-client.service}}
 +
 
 +
=== SASL authentication ===
 +
Add a user to the SASL database for SMTP authentication.
 +
# saslpasswd2 -c your-username
 +
 
 +
== Tips and tricks ==
 +
=== Forward all the mail of one domain to certain user ===
 +
To forward all mail addressed to any user in the '''my-other.tk''' domain to '''your-username@your-domain.com''', add to the {{ic|/etc/mail/virtusertable}} file:
 
{{bc|@my-other.tk        your-username@your-domain.com}}
 
{{bc|@my-other.tk        your-username@your-domain.com}}
* Then process it with
+
 
{{bc|makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable}}
+
Do not forget to process it again with  
 +
# makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable

Latest revision as of 22:33, 19 May 2016

Sendmail is the classic SMTP server from the unix world. Arch Linux provides the alternative Postfix in the official repositories.

The goal of this article is to setup Sendmail for local users accounts, without using mysql or other database, and allowing also the creation of mail-only accounts.

This article only explains the required steps configuring Sendmail; after that, you probably want to add IMAP and POP3 access, so you could follow the Dovecot article.

Installation

Install the sendmailAUR, procmail and m4 packages.

DNS Records

You should have a domain, and edit your MX records to point your server. Remember some servers have problems with MX records pointing to CNAMEs, so your MX should point to an A record instead.

Adding users

Create a Linux user for each user that wants to receive email at username@your-domain.com. To add mail-only accounts, that is, users who can get email, but can't have shell access or login on X, you can add them like this:

# useradd -m -s /usr/bin/nologin username

Configuration

Create SSL certs

Warning: If you plan on implementing SSL/TLS, know that some variations and implementations are still vulnerable to attack. For details on these current vulnerabilities within SSL/TLS and how to apply appropriate changes to Sendmail, visit http://disablessl3.com/ and https://weakdh.org/sysadmin.html

Generate a key and obtain a certificate. See OpenSSL#Self-signed certificate for private use or Let's Encrypt for a free publicly-trusted certificate.

sendmail.cf

Create the file /etc/mail/sendmail.mc. You can read all the options for configuring sendmail on the file /usr/share/sendmail-cf/README.

Warning: If you create your own sendmail.mc file, remember that plaintext auth over non-TLS is very risky. Using the following example forces TLS and is therefore more safe unless you know what are you doing

Here is an example using auth over TLS. The example has comments explaing how it works. The comments start with dnl .

/etc/mail/sendmail.mc
include(`/usr/share/sendmail-cf/m4/cf.m4')
define(`confDOMAIN_NAME', `your-domain.com')dnl
FEATURE(use_cw_file)
dnl  The following allows relaying if the user authenticates,
dnl  and disallows plaintext authentication (PLAIN/LOGIN) on
dnl  non-TLS links:
define(`confAUTH_OPTIONS', `A p y')dnl
dnl
dnl  Accept PLAIN and LOGIN authentications:
TRUST_AUTH_MECH(`LOGIN PLAIN')dnl
define(`confAUTH_MECHANISMS', `LOGIN PLAIN')dnl
dnl
dnl Make sure this paths correctly point to your SSL cert files:
define(`confCACERT_PATH',`/etc/ssl/certs')
define(`confCACERT',`/etc/ssl/cacert.pem')
define(`confSERVER_CERT',`/etc/ssl/certs/server.crt')
define(`confSERVER_KEY',`/etc/ssl/private/server.key')
dnl
FEATURE(`virtusertable', `hash /etc/mail/virtusertable.db')dnl
OSTYPE(linux)dnl
MAILER(local)dnl
MAILER(smtp)dnl

Then process it with

# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

local-host-names

Put your domains on the local-host-names file:

/etc/mail/local-host-names
localhost
your-domain.com
mail.your-domain.com
localhost.localdomain

Make sure the domains are also resolved by your /etc/hosts file.

access.db

Create the file /etc/mail/access and put there the base addresses where you want to be able to relay mail. Lets suppose you have a vpn on 10.5.0.0/24, and you want to relay mails from any ip in that range:

/etc/mail/access
10.5.0 RELAY
127.0.0 RELAY

Then process it with

# makemap hash /etc/mail/access.db < /etc/mail/access

aliases.db

Edit the file /etc/mail/aliases and uncomment the line #root: human being here and change it to be like this:

root:         your-username

You can add aliases for your usernames there, like:

coolguy:      your-username
somedude:     your-username

Then process it with

# newaliases

virtusertable.db

Create your virtusertable file and put there aliases that includes domains (useful if your server is hosting several domains)

/etc/mail/virtusertable
your-username@your-domain.com         your-username
joe@my-other.tk                       joenobody

Then process it with

# makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable

Start on boot

Enable and start the following services. Read Daemons for more datails.

  • saslauthd.service
  • sendmail.service
  • sm-client.service

SASL authentication

Add a user to the SASL database for SMTP authentication.

# saslpasswd2 -c your-username

Tips and tricks

Forward all the mail of one domain to certain user

To forward all mail addressed to any user in the my-other.tk domain to your-username@your-domain.com, add to the /etc/mail/virtusertable file:

@my-other.tk        your-username@your-domain.com

Do not forget to process it again with

# makemap hash /etc/mail/virtusertable.db < /etc/mail/virtusertable