SMTP, the Simple Mail Transfer Protocol, is the set of rules computers use to send email. Whenever someone in Kingston emails a supplier in Miami, or a website in Ocho Rios sends a booking confirmation to a guest in Toronto, SMTP carries the message from one server to the next until it reaches the recipient’s mailbox provider. For a short definition, see our glossary entry on SMTP.
How an email travels
- Your software creates the message: an email program, a website form or an accounting system.
- It connects to an outgoing SMTP server and authenticates, usually with a username and password.
- The SMTP server looks up the recipient’s domain to find which server accepts mail for it.
- It delivers the message to that server, which checks it for spam and authentication before placing it in the inbox, the spam folder, or rejecting it.
Receiving mail is handled by other protocols, IMAP and POP3. SMTP is only about sending.
Ports and encryption
SMTP connections use specific network ports. Port 587 with STARTTLS and port 465 with implicit TLS are the usual choices for authenticated sending today; port 25 is mainly used between mail servers and is often blocked by internet providers for ordinary connections. Our blog explains port 465 vs port 587. Encryption matters: Mailpro secures connections with TLS 1.3, protecting the personal data inside your messages in transit.
Why website emails end up in spam
Many Jamaican businesses host their website on a shared server that also sends email. Hundreds of other sites may use the same server’s IP address, and if any of them send spam, everyone’s messages suffer. Missing authentication makes it worse. Gmail, Outlook and Yahoo increasingly reject or filter messages from domains without SPF, DKIM and DMARC records. The fix is to send through a reputable relay with proper authentication, using correctly configured deliverability routing.
SMTP terms you’ll come across
- Relay: a server that accepts your messages and passes them on for delivery.
- Bounce: a message returned because it couldn’t be delivered. A hard bounce is permanent, a soft bounce temporary.
- SPF, DKIM, DMARC: DNS records that prove your domain authorised the sending server and that the message wasn’t altered.
- Envelope sender: the technical return address used for bounces, which can differ from the “From” address people see.
- Rate limit: the maximum number of messages a server accepts in a given period, which matters when a website sends many confirmations at once.
SMTP relay vs your own mail server
Some organisations run their own mail servers. That gives control, but also responsibility for security updates, IP reputation, bounce handling and blacklist monitoring. For most small and medium Jamaican businesses, a managed relay such as the Mailpro SMTP server is simpler and more reliable.
SMTP and the law
SMTP is just the transport; the content still has to follow the rules. Under Jamaica’s Data Protection Act, 2020, promotional emails require consent or an existing customer relationship with a free opt-out, and personal data must be kept secure and only transferred to countries with adequate protection. Mailpro processes data in Switzerland, outside US jurisdiction.
SMTP or API?
If your software already supports SMTP, it is the quickest way to connect. If you are building a new application and want per-message tracking, an API may suit you better. Compare the options in API vs SMTP, and see what you can measure in SMTP statistics.