The latest articles on DEV Community by Ashish Tiwari (@heyashish). https://dev.to/heyashish https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.us-east-2.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F4002781%2Ffd10c975-72e6-4b91-9654-eee2c665e43e.jpeg https://dev.to/heyashish en Ashish Tiwari Thu, 25 Jun 2026 17:17:11 +0000 https://dev.to/heyashish/building-my-own-mail-server-on-aws-and-getting-blocked-by-port-25-18l9 https://dev.to/heyashish/building-my-own-mail-server-on-aws-and-getting-blocked-by-port-25-18l9 <h1> Building My Own Mail Server on AWS (And Getting Blocked by Port 25) </h1> <p>Email is something we all use every day.</p> <p>Click <strong>Send</strong>, wait a second, and somehow the message lands in someone else's inbox. It feels simple.</p> <p>Until you decide to build the entire thing yourself.</p> <p>That's exactly what I did.</p> <p>My original goal wasn't to create a production-ready mail server. I simply wanted to understand what actually happens after pressing the <strong>Send</strong> button.</p> <p>So I spun up an EC2 instance, installed <strong>Postfix</strong> and <strong>Dovecot</strong>, bought a domain, and started experimenting.</p> <h2> The Plan </h2> <p>The plan sounded straightforward.</p> <ul> <li>Install Postfix</li> <li>Configure Dovecot</li> <li>Point my domain's DNS records</li> <li>Send my first email</li> </ul> <p>Easy... right?</p> <p>Not exactly.</p> <p>Everything went smoothly until I tried sending an email.</p> <p>Nothing happened.</p> <p>After spending a while checking logs and configurations, I discovered the real culprit.</p> <p>AWS blocks outbound traffic on <strong>port 25</strong> by default to prevent spam.</p> <p>So my mail server reached a very interesting state.</p> <p>It can receive emails perfectly.</p> <p>It just can't send them.</p> <p>I've already submitted a request to AWS to unblock port 25, so for now my mail server is patiently waiting for permission to speak.</p> <h2> The Rabbit Hole </h2> <p>What I expected to be a small weekend project quickly became one of the most educational side projects I've worked on.</p> <p>I finally understood the difference between <strong>SMTP</strong> and <strong>IMAP</strong>.</p> <p>SMTP is responsible for sending emails between servers.</p> <p>IMAP allows clients like Gmail or Outlook to synchronize your mailbox across devices.</p> <p>I also learned why DNS is one of the most important parts of email.</p> <p>Without properly configured records, your mail server simply doesn't exist as far as other servers are concerned.</p> <h2> Understanding DNS Records </h2> <p>Building the server forced me to work with several DNS records that I had previously only heard about.</p> <h3> MX Records </h3> <p>MX records tell the internet where emails for your domain should be delivered.</p> <p>Without them, other mail servers have no idea where your inbox lives.</p> <h3> SPF </h3> <p>SPF specifies which servers are allowed to send emails on behalf of your domain.</p> <p>It helps reduce spoofing.</p> <h3> DKIM </h3> <p>DKIM digitally signs outgoing emails so receiving servers can verify they haven't been modified during transit.</p> <h3> Reverse DNS </h3> <p>Many mail providers also verify reverse DNS records before trusting your server.</p> <p>Missing this configuration often leads to emails being marked as spam.</p> <h2> Email Is Basically a Digital Post Office </h2> <p>One realization made everything click.</p> <p>Email works surprisingly similar to the Indian Post Office.</p> <p>Your domain acts like the address.</p> <p>DNS works like the directory that tells everyone where your house is.</p> <p>MX records point to the correct delivery office.</p> <p>SMTP transports the letter.</p> <p>IMAP lets you visit your mailbox whenever you want.</p> <p>Once I started thinking about email this way, the entire system suddenly made sense.</p> <h2> What I Learned </h2> <p>This project taught me much more than how to configure Postfix.</p> <p>It helped me understand:</p> <ul> <li>How SMTP and IMAP work together</li> <li>Why DNS configuration is critical</li> <li>How MX, SPF and DKIM improve email delivery</li> <li>How mail servers discover one another</li> <li>Why running a reliable mail server is much harder than it first appears</li> </ul> <h2> What's Next? </h2> <p>The immediate goal is getting AWS to approve outbound access on port 25.</p> <p>Once that happens, I'll configure secure email delivery with TLS, improve spam protection, and experiment with running a fully functional self-hosted mail server.</p> <h2> Final Thoughts </h2> <p>Nobody asked me to build a mail server.</p> <p>There are plenty of hosted email providers that solve this problem much better than I ever could.</p> <p>I built it simply because I was curious.</p> <p>That's one of the things I love most about software engineering.</p> <p>Sometimes the best projects aren't the ones that solve a business problem.</p> <p>They're the ones that answer a question you've been wondering about for a long time.</p> <p>This project may not replace Gmail anytime soon, but it definitely replaced a lot of "I wonder how that works?" with "Now I know."</p> <p>Originally published on my portfolio:<br> <a href="https://ashishtiwari.dev" rel="noopener noreferrer">https://ashishtiwari.dev</a></p> aws learning networking tutorial