SMTP stands for Simple Mail Transfer Protocol. It is the set of rules mail servers use to pass messages to each other, and it has been the backbone of email since the early 1980s. Every email your business in Saint Vincent and the Grenadines sends, whether a newsletter, an invoice or a quick reply, travels by SMTP at some point.

Following one email

Imagine a charter company in Union Island sends a booking confirmation to a guest in Toronto.

  1. The company’s booking software connects to an SMTP server, often called the outgoing mail server, and logs in.
  2. It hands over the message: sender, recipient, subject and content.
  3. The SMTP server looks up the recipient’s domain in the DNS to find which server accepts mail for it (the MX record).
  4. It connects to that server and transfers the message.
  5. The receiving server checks the sender’s authentication and reputation, then files the message in the inbox, the junk folder or rejects it.
  6. The guest opens it using a different protocol, IMAP or POP3, to read their mailbox.

SMTP handles sending and transfer; it does not handle reading. The FAQ on the difference between SMTP, IMAP and POP3 explains the three.

Ports you will see

  • 587: the standard port for submitting mail from software, with STARTTLS encryption.
  • 465: SMTP over TLS from the start, also widely supported.
  • 25: used between servers; often blocked for ordinary internet connections to stop spam.

Our article on port 465 vs port 587 goes into the details.

Why authentication decides the inbox

SMTP was designed at a time when everyone on the network was trusted, so by itself it does not verify who is sending. Three DNS records fill that gap:

  • SPF lists the servers allowed to send for your domain.
  • DKIM adds a cryptographic signature proving the message was not altered.
  • DMARC tells receiving servers what to do if SPF or DKIM fail, and sends you reports.

Gmail, Yahoo and Microsoft now expect bulk senders to have these in place. See our SMTP definition and the glossary entries for each record.

Spoofing and the law in SVG

Because basic SMTP does not verify senders, criminals can try to forge them, which is behind many phishing emails. SVG’s Cybercrime Act 2016 includes offences covering spam sent to mislead recipients about its origin, falsified headers and spoofing. Authentication records protect your domain from being impersonated, and your customers from being fooled.

Using an SMTP relay

A relay is an SMTP server run by a specialist, which accepts your software’s mail and delivers it on your behalf with good reputation, authentication and logging. That is what Mailpro’s SMTP server provides, with TLS 1.3 encryption and data hosted in Switzerland. It is often the simplest fix when website or invoice emails keep landing in junk.

Common SMTP problems in small offices

  • Emails sent from the website never arrive: the site is sending through the web host’s shared server without authentication. Switch to an authenticated relay.
  • “Relay access denied”: the software is not logging in, or is using the wrong username or port.
  • Connection timeouts: the software is trying port 25, which your internet provider may block. Use 587 or 465.
  • Messages marked as spam: SPF, DKIM or DMARC are missing or incorrect.

SMTP or API?

If you are building an application, an HTTP API may be a better fit than SMTP. Read API vs SMTP for a comparison.

Reliable SMTP for your Saint Vincent and the Grenadines applications

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