How to make your own mail server and avoid getting your mail in spam?

You need to send your emails with a proper DKIM, DMARC and SPF signification!

Postfix

• Install all required software:

apt-get install opendkim opendkim-tools postfix-policyd-spf-python postfix-pcre
sudo adduser postfix opendkim

Opendkim

Configure opendkim

• Create a opendkim keys directory:

mkdir -p /etc/opendkim/keys

• Generate a keys:

export DOMAIN=burlutsky.su

cd /etc/opendkim/keys/
mkdir $DOMAIN
cd $DOMAIN
opendkim-genkey -s mail -d $DOMAIN

Here is a mail selector name. Replace burlutsky.su with your domain name.

• Create your signing table:

cat >>/etc/opendkim/SigningTable <<EOF
*@$DOMAIN mail._domainkey.$DOMAIN

cat /etc/opendkim/TrustedHosts 
127.0.0.1
localhost

$DOMAIN
*.$DOMAIN
EOF

• Create a key table:

cat > /etc/opendkim/KeyTable <<EOF
mail._domainkey.$DOMAIN $DOMAIN:mail:/etc/opendkim/keys/$DOMAIN/mail.private

• Add your files definition to the /etc/opendkim.conf file:

AutoRestart             Yes
AutoRestartRate         10/1h
SyslogSuccess           Yes
LogWhy                  Yes
Canonicalization        relaxed/simple

ExternalIgnoreList      refile:/etc/opendkim/TrustedHosts
InternalHosts           refile:/etc/opendkim/TrustedHosts
KeyTable                refile:/etc/opendkim/KeyTable
SigningTable            refile:/etc/opendkim/SigningTable
Mode                    sv
Socket                  inet:12301@localhost

• Enable opendkim daemon running on the localhost TCP socket. Change: /etc/defaults/opendkim

SOCKET="inet:12301@localhost"

• Add new postfix milter with the opendkim socket. Add to /etc/postfix/main.cf:

milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301

policyd-spf_time_limit = 3600
smtpd_helo_required = yes
smtpd_recipient_restrictions =
    permit_mynetworks,
    permit_sasl_authenticated,
    reject_unauth_destination,
    check_policy_service unix:private/policyd-spf

smtp_tls_security_level = may
smtp_tls_ciphers = export
smtp_tls_protocols = !SSLv2, !SSLv3
smtp_tls_loglevel = 1

• Set permissions:

chown -R opendkim:opendkim /etc/opendkim

• Edit /etc/postfix/master.cf and add the following entry at the end:

policyd-spf  unix  -       n       n       -       0       spawn
    user=policyd-spf argv=/usr/bin/policyd-spf

• Enable and start services:

systemctl enable postfix
systemctl restart postfix
systemctl enable opendkim
systemctl restart opendkim

DNS

Now we need to configure DNS system. Add all DNS records below:

• SPF record.

TXT "v=spf1 a:burlutsky.su -all"

replace burlutsky.su with your domain.

• Now you need to get a DKIM key.

cat /etc/opendkim/keys/$DOMAIN/mail.txt 

You can see something like this:

mail._domainkey IN      TXT     ( "v=DKIM1; h=sha256; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAq+...)  ; ----- DKIM key mail 

Add this text record to the DNS system.

• Turn on DMARC:

_dmarc.burlutsky.su IN TXT "v=DMARC1; p=none; sp=none;"

• Test your email with gmail or online services like this: https://mxtoolbox.com/dkim.aspx . Set selector = mail .