SMTP Relay Setup Guide (AlmaLinux 8 + cPanel Integration)

PART 1: Setup the SMTP Relay Server (AlmaLinux 8)

Step 1 – Install Postfix

dnf install -y initscripts
dnf install -y postfix
systemctl enable postfix
systemctl start postfix

Step 2 – Configure Postfix as a Relay Host

nano /etc/postfix/main.cf

myhostname = eostre.names4u.win
mydestination =
relay_domains = *
mynetworks = 127.0.0.0/8, 163.61.30.92/32
inet_interfaces = all
inet_protocols = ipv4

systemctl restart postfix

postfix check

No output means the configuration is valid. Your AlmaLinux VPS now acts as a basic relay, accepting mail only from your cPanel server IP.

Step 3 – Confirm Postfix Settings

postconf mynetworks

mynetworks = 127.0.0.0/8, 163.61.30.92/32

Step 4 – Verify Listening Ports

ss -tulpn | grep master

tcp LISTEN 0 100 0.0.0.0:25 0.0.0.0:* users:(("master",pid=1234,fd=13))

grep -E '^[^#].*(smtp|submission)' /etc/postfix/master.cf

smtp inet n - n - - smtpd
submission inet n - n - - smtpd

• smtp → Port 25 is active
• submission → Port 587 is active (if not commented)

(Optional) Enable Port 587

nano /etc/postfix/master.cf

submission inet n - n - - smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=may
  -o smtpd_sasl_auth_enable=no
  -o smtpd_relay_restrictions=permit_mynetworks,reject_unauth_destination
  -o smtpd_recipient_restrictions=permit_mynetworks,reject_unauth_destination

systemctl restart postfix

ss -tulpn | grep master

tcp LISTEN 0 100 0.0.0.0:25
tcp LISTEN 0 100 0.0.0.0:587

PART 2: Configure the cPanel Server (Crater)

Step 5 – Update Exim Route

smarthost_route:
  driver = manualroute
  domains = ! +local_domains
  transport = remote_smtp
  route_list = * eostre.names4u.win::587
  no_more

Step 6 – Test the Connection

nc -vz eostre.names4u.win 587

Connection to eostre.names4u.win 587 port [tcp/submission] succeeded!

exim -qf
tail -f /var/log/exim_mainlog

tail -f /var/log/maillog

You should see your relay accepting connections from the cPanel server and queuing mail.

/scripts/buildeximconf
/scripts/restartsrv_exim

echo "Relay test successful" | mail -s "Relay Test" [email protected]

PART 3: Configure SPF Records

Step 7 – Create Central SPF Include

dig txt _spf.names4u.win

"_spf.names4u.win. IN TXT "v=spf1 ip4:163.61.30.92 ip4:173.249.215.35 +a +mx ~all""

Step 8 – Automatic SPF for New Domains

nano /usr/local/cpanel/etc/zonetemplates/standard

%domain%. IN TXT "v=spf1 include:_spf.names4u.win ~all"

/usr/local/cpanel/etc/zonetemplates/standardvirtualftp

/scripts/rebuilddnsconfig

From now on, every new or addon domain will include the unified SPF record automatically.

Step 9 – Update SPF for Existing Domains

9.1 List All cPanel Accounts

whmapi1 listaccts --output=json | jq -r '.data.acct[].domain'

9.2 Update SPF in Zone Files

for domain in $(whmapi1 listaccts --output=json | jq -r '.data.acct[].domain'); do
  zonefile="/var/named/${domain}.db"
  if [ -f "$zonefile" ]; then
    cp "$zonefile" "$zonefile.bak"
    if grep -q 'v=spf1' "$zonefile"; then
      sed -i 's/v=spf1.*/v=spf1 include:_spf.names4u.win ~all"/' "$zonefile"
      echo "Updated SPF in $domain"
    else
      echo "$domain. IN TXT \"v=spf1 include:_spf.names4u.win ~all\"" >> "$zonefile"
      echo "Added SPF to $domain"
    fi
  else
    echo "No local zone file for $domain (managed by DNS cluster or Cloudflare)"
  fi
done

9.3 Restart PowerDNS

systemctl restart pdns

9.4 Sync to DNS Cluster

/scripts/dnscluster syncall

Step 10 – Verification

10.1 Local Check

dig txt adiyanbd.com @127.0.0.1

"v=spf1 include:_spf.names4u.win ~all"

10.2 Global Check (After TTL ~4 hours)

dig txt adiyanbd.com @8.8.8.8

Step 11 – For Domains on Cloudflare or External DNS

cPanel cannot update DNS automatically for such domains.

• AlmaLinux VPS is configured as a secure SMTP relay.
• cPanel server routes mail via this relay.
• SPF is centralized and auto-managed for all domains.