SMTP stands for Simple Mail Transfer Protocol., it has been around for some time but remains to be one of the best email sending protocols. SMTP is the protocol that sends the emails, the protocol requires an email client and a host server. This transfer of emails vis SMTP is known as an SMTP relay service.
Most commonly for individuals, using mailboxes like Gmail and Hotmail is sufficient as they allow a person to send up to 500 emails per day. But for a business with a subscriber or customer base in the thousands, it becomes quite tough to send emails. This is where a professional SMTP relay service provider comes in. Some of the most preferred services include Pepipost, SendinBlue, Sparkpost, etc
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How Does an SMTP Relay Work?
When an email is sent from your computer, your email client sends your email to its destination over the SMTP protocol. The SMTP server then looks up the destination of the email and transmits the email to the server closest to/ to the destination server. This server then looks up the email domain and passes your email onto the next email server. The mail server of the recipient then stores the email and keeps it ready for the email client of the recipient to collect it. The recipient collects the email from the mail server using a mail client that uses the protocol POP3 or IMAP (or webmail using a web browser)
This can be understood better by the most common example of sending a letter when you send a letter with a correct address on it, you drop it off at your nearest post office. The post office then transfers all the letters in a hub, sorts the letters by their destination and sends it to the respective hubs. These hubs then further bifurcate the letters based on addresses until the letter reaches the letterbox of the recipient who collects it from their letterbox.
When your server knows the IP address of your recipients’ email server, it will attempt to connect to this server on the SMTP port. Port 25 for SMTP is the most commonly used port for sending emails online.
When connected, your server will say “Hello, I have an email for ‘email@example.com'”. The SMTP email server at uber.com then replies saying “OK, please start the transmission of your email”. This is also an important part of transmission so that during information exchange, none of the important information is lost.
If the server isn’t responsible for receiving email for uber.com, it will inform your server causing it to return the email with an error. These errors can happen when your server is using a DNS server that is not up-to-date. It is therefore very important that your server uses the correct DNS server. You should be careful and consider all the factors before choosing a DNS server.
In some cases, your email server doesn’t need to do the DNS/MX lookup. These are the cases where you have a smart host your server can forward all it’s outbound emails to. A smart host will then either do the DNS/MX lookups itself or forward the message to another server/host to do the DNS/MX lookup.
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The SMTP relay is a simple yet effective way to send emails in a secure and efficient manner over the internet. Doe to the large use of this protocol, there is also very little infrastructure expenditure.
This was a basic idea of how the protocol works. We will be sharing more articles on how the protocol. Do let us know what you think of the article in the comments below.