How to send email from the server and not get into spam
Sometimes people need to send email from their apps. You can use Amazon SES (very cheap), Mailchimp (more expensive), etc. But if you want to send an email for free, you will need to send an email from your server. When you start to send emails from your server, you will be sure to get into spam. This article will help to avoid this.
What I want
- Sending emails from the server
- Pass spam filters
- Free sending
- Sending only (without receiving emails)
Installing postfix
apt update
apt install mailutils -y
Select Internet Site. And write your domain in the next step. For example, I will use example.com
SPF
Create txt record
v=spf1 include:_spf.google.com ip4:IP_SERVER ~all
DKIM
apt install opendkim opendkim-tools
mkdir /etc/postfix/dkim/
# Generate key for server
opendkim-genkey -D /etc/postfix/dkim/ -d example.com -s mail
Folder /etc/postfix/dkim/ will have 2 files mail.private and mail.txt (private and public keys)
We must change permission to private key
# Set permission
chmod 600 /etc/postfix/dkim/mail.private
# Change folder owner
chown -R opendkim /etc/postfix/dkim/
Edit file /etc/opendkim.conf to look like this:
Syslog yes
Domain *
Selector mail
Socket inet:8891@localhost
Mode sv
# Set list of keys
KeyTable file:/etc/postfix/dkim/keytable
# Match keys and domains
SigningTable file:/etc/postfix/dkim/signingtable
File /etc/postfix/dkim/keytable must has information about private key:
# key_name domain:selector:/path/to/ley
mail._domainkey.example.com example.com:mail:/etc/postfix/dkim/mail.private
File /etc/postfix/dkim/signingtable has list of domains what need to sign:
# domain key_name
example.com mail._domainkey.example.com
File /etc/default/opendkim must has rule about SOCKET, which will listen opendkim (other rules about SOCKET necessary remove):
SOCKET="inet:8891@localhost"
Little bit changes in Postfix config file /etc/postfix/main.cf:
# myhostname must has right value
myhostname = example.com
# This rule because we don't want receiving emails
mydestination = localhost
# Add in end file
milter_default_action = accept
milter_protocol = 2
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891
You must sure what this file /etc/mailname look like this
example.com
Restarting postfix and opendkim:
service postfix restart
service opendkim restart
DNS
Creating A record for a subdomain
тип: A
имя: mail._domainkey
указатель: IP_SERVER
TTL: 300
Take data from /etc/postfix/dkim/mail.txt and creating another TXT record
тип: TXT
имя: mail._domainkey
указатель: v=DKIM1; k=rsa; p=MI***
TTL: 300
Testing
We can check on DKIM work with utility opendkim-testkey
opendkim-testkey -d example.com -s mail -vvv
# Good result
opendkim-testkey: using default configfile /etc/opendkim.conf
opendkim-testkey: checking key 'mail._domainkey.example.com'
opendkim-testkey: key not secure
opendkim-testkey: key OK
Great! Your email server working now. But sometimes these actions are not enough. And your mail still catches into spam. This site can helps you.
Send an email from your server to mail-tester. And fix errors which mail-tester find.
echo "Test Email message body" | mail -s "Email test subject" -aFrom:testemail@example.com besthopox@gmail.com
When writing the article, I used next materials: