Receiving email (online)

This comes in two parts, configured at the domain/DNS level:

1. A record: maps "mail.pokey.onl" to VPS IP
2. MX record: maps mail to "mail.pokey.onl"

In my case, my email-specific DNS configuration looks like this:

I also want to configure a PTR Record at the VPS provider level. This is designed to work in the reverse direction of the A record by mapping the VPS IP to the mail server's domain name. With Akamai, I navigated to my Linode, then Network > IP Addresses > Edit RDNS > insert "mail.pokey.onl".

After defining the routing information, I took a break to wait for the necessary propagation. Now, we can see that the records are set properly.

Using dig mail.pokey.onl (checking A record):

mail.pokey.onl.		600	IN	A	96.126.120.46

Using dig MX pokey.onl (checking MX record):

pokey.onl.		600	IN	MX	10 mail.pokey.onl.

Using dig -x 96.126.120.46 (checking PTR record):

46.120.126.96.in-addr.arpa. 295	IN	PTR	mail.pokey.onl.

Surprisingly, it was the PTR record which took the longest to propagate in my case.

Finally, we can begin running the actual SMTP server. I transferred my files to the VPS, installed gcc through the build-essentials package, and then compiled the project.

I ran the server for the first time using the following command:

./server & echo $! > mves.pid

Then, from my laptop terminal, trying to telnet into the SMTP server (telnet mail.pokey.onl 25) gives me Trying 96.126.120.46..., but this never connects even though (on the VPS) I see the expected entry using socket statistics (ss -tulnp | grep :25).

As a result, I am fairly certain that these ports were being blocked prior to reaching my VPS. Following the warning message I received from Linode at the VPS creation, I filed a ticket to remove the SMTP port restriction early in the morning on March 27, 2026.

After less than 6 hours, my ticket was approved, but I still couldn't telnet into the server. As it turns out, the issue here was with my local machine: my home network was apparently blocked from sending on port 25, but as soon as I switched to a mobile hotspot, my requests to the server could go through.

With this setup and issues resolved, I was now able to send my first email over the internet to the email server:

% telnet mail.pokey.onl 25
Trying 96.126.120.46...
Connected to mail.pokey.onl.
Escape character is '^]'.
220 mail.pokey.onl Simple Mail Transfer Service Ready
EHLO mail.pokey.onl
250-mail.pokey.onl greets mail.pokey.onl
250-SIZE 100000
250 VRFY
MAIL FROM:<alice@pokey.onl>
250 OK
RCPT TO:<bob@pokey.onl>
250 OK
DATA
354 Start mail input; end with <CRLF>.<CRLF>
Hello Bob, this is a test message over the internet!
.
250 OK
QUIT
221 mail.pokey.onl Service closing transmission channel
Connection closed by foreign host.

As a result of this communication, the email server wrote "1774645958.10644.mail.pokey.onl" to "./mail/bob/Maildir/new". This is a important milestone for this project!

Here is a summary of the progress so far:

*The Internet Message Format is a standard for headers and content sent within DATA of SMTP. This is supported but only as arbitrary data at this point.

Last updated March 28, 2026