SMTP, the Simple Mail Transfer Protocol, is the standard that email servers use to send messages to one another. Every email you send, whether from Outlook in a Valletta office or from a booking engine in a data centre, travels using SMTP. The glossary has a short SMTP definition; this page explains how it works in practice.
The journey of an email
- Submission: your mail client or application connects to an SMTP server (the “relay”) and hands over the message after authenticating.
- Lookup: the relay looks up the recipient domain’s MX records in DNS to find its mail server.
- Transfer: the relay connects to that server and transfers the message, ideally over an encrypted connection.
- Delivery: the receiving server checks authentication and reputation, then places the message in the inbox, the spam folder, or rejects it.
- Retrieval: the recipient reads it using IMAP, POP3 or webmail. Those protocols are for reading; SMTP is only for sending. See SMTP vs IMAP vs POP3.
Ports you will meet
- 587: the standard submission port, using STARTTLS to upgrade to encryption.
- 465: SMTP over implicit TLS, also widely used.
- 25: server-to-server transfer; many ISPs block it for end users.
Our article on port 465 vs port 587 goes deeper.
Authentication: proving you are you
SMTP itself is old and trusting. Modern mailbox providers rely on three DNS records to judge whether a message is genuine: SPF lists which servers may send for your domain, DKIM signs messages cryptographically, and DMARC tells receivers what to do with failures. Without them, mail from your .mt or .com domain is far more likely to be junked. Mailpro’s guide to SPF, DKIM and DMARC explains setup.
Why the relay’s location matters in Malta
An SMTP relay processes the full content of your emails, including names, addresses and whatever is in the message. Under GDPR, choosing a relay outside the EU is a data transfer that needs a lawful basis. Mailpro’s relay runs on private infrastructure in Switzerland, which benefits from an EU adequacy decision, and outside US jurisdiction, so Maltese organisations can use it without additional transfer mechanisms. The IDPC is the authority that would examine such arrangements in Malta.
Common SMTP errors
SMTP servers reply with numeric codes. Codes starting with 2 mean success, 4 means a temporary problem worth retrying, and 5 means a permanent failure such as an unknown mailbox. If your application logs a 5xx error, check the address and your authentication. The common SMTP errors FAQ lists the codes you are most likely to see.
When a business needs its own SMTP relay
If you send from a website, CRM, ERP, accounting package or custom application, a managed relay improves delivery and gives you logs. It suits Maltese hotels with booking engines, e-commerce stores, gaming and fintech platforms, and any firm sending invoices by email.
Ready to set one up? See SMTP server for Malta and the SMTP sending server features.