Theory & Background

Before sending any mail: set all DNS records. MX record: @ IN MX 10 mail.catb.in (points to your server). A record: mail.catb.in → your_server_ip. PTR record (reverse DNS): ask VPS provider to set IP → mail.catb.in. SPF TXT record: v=spf1 mx a ~all. DKIM: generate keys with OpenDKIM, add TXT record at selector._domainkey.catb.in. DMARC TXT record: _dmarc.catb.in v=DMARC1; p=reject; rua=mailto:dmarc@catb.in. Without these records, your email will be marked as spam or rejected.

Components & Requirements

10 components required for this project.

#	Component	Purpose	Qty
1	VPS (Ubuntu 22.04, static IP, reverse DNS)	Email server host	x1
2	Domain name (catb.in)	Email domain	x1
3	Postfix MTA	Mail Transfer Agent (sending/receiving)	x1
4	Dovecot IMAP server	Mail delivery and IMAP/POP3	x1
5	SpamAssassin	Spam filtering	x1
6	ClamAV	Email virus scanning	x1
7	OpenDKIM	DKIM email signing	x1
8	Roundcube Webmail	Browser-based email client	x1
9	Rspamd (alternative spam filter)	Modern, faster spam filter	x1
10	MailHog (testing)	Email testing without sending real mail	x1

Step-by-Step Implementation

Follow these 3 steps carefully.

1

DNS Records for Email (Critical)

Before sending any mail: set all DNS records. MX record: @ IN MX 10 mail.catb.in (points to your server). A record: mail.catb.in → your_server_ip. PTR record (reverse DNS): ask VPS provider to set IP → mail.catb.in. SPF TXT record: v=spf1 mx a ~all. DKIM: generate keys with OpenDKIM, add TXT record at selector._domainkey.catb.in. DMARC TXT record: _dmarc.catb.in v=DMARC1; p=reject; rua=mailto:dmarc@catb.in. Without these records, your email will be marked as spam or rejected.

2

Postfix and Dovecot Configuration

Postfix (MTA): handles sending and receiving SMTP. Configure main.cf: myhostname=mail.catb.in, mydomain=catb.in, mynetworks=127.0.0.1 (only allow local relay), smtpd_tls_cert_file=Let's Encrypt cert (TLS required), smtpd_sasl_auth_enable=yes (SMTP authentication with Dovecot SASL). Dovecot (MDA): handles IMAP/POP3, delivers mail to mailboxes. Configure mail_location, ssl_cert/key, auth mechanisms (PLAIN over TLS only), userdb/passdb (system users or MySQL).

3

Anti-Spam and Email Security

Rspamd: modern spam filter with machine learning. Actions: reject (very high spam score), add spam header (medium score), accept (low score). DKIM signing: all outbound mail signed with private key — recipients can verify authenticity. SPF: receiving servers check if your IP is authorized to send for your domain. DMARC: tells receivers what to do if SPF/DKIM fail (reject/quarantine/none) and where to send aggregate reports. Check score on mail-tester.com (aim for 10/10).

Code & Implementation

Core code for email_server_test.sh:

email_server_test.sh
  Shell

#!/bin/bash # Email server configuration verification  DOMAIN="catb.in" MAIL_HOST="mail.catb.in"  echo "=== DNS Records Check ===" echo "MX record:"    ; dig $DOMAIN MX +short echo "SPF record:"   ; dig $DOMAIN TXT +short | grep spf echo "DMARC record:" ; dig _dmarc.$DOMAIN TXT +short echo "PTR record:"   ; dig -x $(dig $MAIL_HOST A +short | head -1) +short  echo "\\n=== Port Checks ===" nc -zv $MAIL_HOST 25  2>&1 | grep -c "succeeded" && echo "SMTP (25): OPEN" || echo "SMTP (25): CLOSED" nc -zv $MAIL_HOST 587 2>&1 | grep -c "succeeded" && echo "SUBMISSION (587): OPEN" nc -zv $MAIL_HOST 993 2>&1 | grep -c "succeeded" && echo "IMAPS (993): OPEN"  echo "\\n=== TLS Certificate ===" echo | openssl s_client -connect $MAIL_HOST:993 2>/dev/null | openssl x509 -noout -dates  echo "\\n=== Test SMTP Connection ===" telnet $MAIL_HOST 25

Testing & Troubleshooting

Test Self-Hosted Email Server by verifying each subsystem individually before full integration.

!

Troubleshooting Tips

Verify power voltages, check ground connections, use serial monitor for debug.

Real-World Applications

*Private family email domain

*Business email independence from Google/Microsoft

*Privacy-focused email communication

*Email list management for newsletter

*Development email testing server

*Corporate email compliance and archive

*Domain-specific email aliases

*Transactional email sending for web apps

Extensions & Next Steps

Add email encryption with S/MIME or PGP auto-key exchange
Implement email list manager (Mailman) for newsletters
Build an AI-powered spam classifier using message history
Add email archiving with search (Elasticsearch)
Implement email delivery analytics dashboard

Interactive Playground

Coming Soon

An interactive simulator will be available here — simulate circuits and run code in-browser without hardware.

Frequently Asked Questions

Why do major providers (Gmail, Outlook) sometimes block email from self-hosted servers?

Email reputation: major providers maintain IP reputation databases and apply machine learning to detect spam sources. New IP addresses have no reputation — treated with suspicion. Getting blocklisted: common for new servers even with perfect configuration. Getting delisted: submit deblocking request to each provider (Google Postmaster Tools, Microsoft JMRP/SNDS). Factors affecting reputation: IP age (new IPs start with neutral reputation), volume (don't send bulk mail initially), content (avoid spam-like subject lines), bounce rate (high bounces indicate purchased lists).

Introduction