Is setting up an Email Server to send-receive emails between email-clients possible over the internet?

Question

Have tried using postfix and claws-mail to accomplish the objective. Failed. I am missing crucial information. Assuming that the ISP I am subscribed to doesn't provide email services or servers for sending-receiving emails, then how to configure personal computers to be used as a server, and use a client such as claws-mail to accomplish the objective? Read this article: Setting Up and Configuring a Linux Mail Server

What it says on email server is actually an email client or a Mail Transport Agent. The real server is Gmail that operates in between two personal computers operating as email clients.

It used the sendmail program to send, receive and store emails, but it requires an email server such as Gmail, between two personal computers operating as email sending-receiving clients.

Could emails be sent from one arbitrary personal computer to another arbitrary personal computer over the internet if:

1. the email-ID of the recipient's computer was known,
2. without any other email server operating in the middle,
3. without my access to another email-server via user-ID and password,
4. but my own personal computer running both a server and a client programs?

In the meanwhile, also read the article:Setting Up and Configuring a Linux Mail Server

My objective is mainly to send emails from my own email-server running from my personal computer. I already have a Gmail account. So sending or receiving emails using the Gmail web interface is normal for me. But sending emails is what I am chiefly interested in. So some aspects like installing spam-assassin could be done away with. dovecot, a secure POP3/IMAP server, is used to configure the set up on this page.

Also reached another article: Simple Method to Install a Mail Server in Linux | Baeldung on Linux This page is simple, using bind9 as a DNS server software.

In all the three webpages, postfix is the one common tool used. I have already installed postfix and tried to configure it partially. I have a hunch that the article in the link 3 shall help me in the set up.

So far so good. In the coming days, shall prepare myself towards a successful set up or an email-server from my own PC.

Of course I know that governments all over the world would probably block such emailing services because of security threats, like terrorists planning and organising an attack. But I just am curious to know if what I described is possible?

In the meantime, Mr. Chris Davies has been kind to inspire me with his optimistic reply to my post. I thank him. In the coming days, with his consent, I shall add to this post further information based on my experience along the way.

More info: My ISP is Reliance Telecom, India, for my smartphone, which I use to access the internet over the 4G mobile network. When I use USB tethering to access the internet, the ifconfig shows varying inet address during different access cycles. However, the good sign is that for internet access through Wireless Hotspot, the inet address remains the same during each access cycles.

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Interactions with support-givers and other posters, chronologically, top down, from oldest to latest:

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Of course it's possible. I run a full mail server at home. You could send me an email directly from your mail server to mine – Chris Davies

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That particular article describes how to set up a Linux based mail server that uses Gmail as its smarthost. That's a common solution but not necessary if you really want the pain of running a public mail server yourself – Chris Davies

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I'm not sure how to answer your question other than with "yes" – Chris Davies

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Thank u, Mr. Davies, for replying to my question. I am not a professional programmer. Learning to use aspects of computing is my hobby, so not adept in terminal, etc. That you can run an email server means I can learn from you, if you're willing to teach. I didn't understand the true nature of your byte, "Gmail as its smarthost". Can I not run a public mail server myself from my computer, switching the device On/Off according to my wish? Pls provide me with the necessary guidance to bridge the gap on know-how required to follow your instructions realise this goal. – Rajibando

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Would you mind, Mr. Davies, if I updated my post with snippets of your bytes? That the above post, "Setting Up and Configuring a Linux Mail Server" used a different email-client (or server) than claws-mail, the one I am familiar with, actually distanced me from its objective. I am easily confused by complex command-line operations. I find myself safer using the GUI tools. But CLI also isn't a problem if the commands are only few. In the meanwhile I tried to understand the Game skimming through a few more articles. – Rajibando

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I understand the question to say that the OP primarily (or maybe exclusively?) wants to exchange messages between clients that are under his control.   If my understanding is correct, will having a “tainted IP address” matter?  IOW, will blacklists matter? – G-Man Says 'Reinstate Monica'

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@Mr. G-man...: Thank you for your question. To add clarity, not "clients that are under his control", but individuals that I know and are in my friend-circle. Having their email-IDs with Gmail, Yahoo and such. Please also be kind to check my Original Post often during this interaction, as I will be updating it often with more info based on my experience. – Rajibando

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@G-ManSays'ReinstateMonica' I read "Could emails be sent from one arbitrary personal computer to another arbitrary personal computer over the internet" to mean any to any – Chris Davies

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@Mr. Davies: Theoretically yes, to illustrate the ambit of my requirement. But not to spam strangers lol:. Only to friends. It would be an interesting learning experience. – Rajibando

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If you want to share messages between friends on a closed system, and not to send/receive messages with providers like Gmail, Microsoft, etc. then all you need is a basic installation of your MTA and something like Dovecot to allow IMAP access to the mail store – Chris Davies

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@Mr. Davies: No, I posted this for Mr. G-man already. "... Having their email-IDs with Gmail, Yahoo and such ..." – Rajibando

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Answer 1

Before you even begin, ask yourself if you really do need to do this. It's not trivial. Non-negotiable mandatory requirements:

• Your mail server must have a fixed public IP address
• You must be able to manage your DNS (and rDNS), either directly or indirectly
• Your ISP must not block traffic on port 25 (SMTP)
• Your IP address must not be on a blacklist (SBL, PBL, etc.)

I'm not going to give a great big tutorial on installation here, as that would be way too broad for Stack Exchange. What I will do is provide one set of applications that should be considered:

• Postfix, Exim4, Sendmail, or some other fully-fledged email system (MTA and optionally MDA, supporting DKIM)
• Dovecot (LDA and IMAP server)
• SpamAssassin (anti-spam)
• ClamAV (anti-virus)

You will also need to set up the following authentication and authorisation declarations in DNS, and for SMTP-TLS on a web server too:

• SPF
• DKIM
• DMARC
• SMTP-TLS

This should give you enough keywords that you can read up on relevant solutions and decide whether or not to go ahead.

But having done all this, if your mail server is using a tainted IP address (for example, in shared VPS space from a provider such as Amazon, Oracle, Google, OVH, DigitalOcean, etc.), your emails will get discarded by the big players anyway. No matter that you've got a perfectly compliant system: your messages just won't get through. IP address quality means a huge amount.