SMTP, the Simple Mail Transfer Protocol, is the standard that email servers use to pass messages to each other. Whenever your website sends an order confirmation, your accountant’s software emails a GST invoice, or you press “send” in Gmail, SMTP is doing the work in the background.
How an email travels
- Submission: your application or mail client connects to an outgoing SMTP server and hands over the message, usually after logging in with a username and password.
- Lookup: the server checks the recipient’s domain (for example, gmail.com or a company domain) in the DNS to find which server accepts its mail.
- Transfer: the sending server connects to the receiving server and passes the message, ideally over an encrypted connection.
- Filtering: the receiving provider checks authentication, reputation and content before deciding whether to deliver to the inbox, the spam folder, or not at all.
- Retrieval: the recipient’s app fetches the message using a different protocol, such as IMAP.
The key terms
- SMTP server or relay: the outgoing server that sends on your behalf.
- Port: the “door” used to connect; submission usually uses port 587 with encryption.
- SPF, DKIM and DMARC: DNS records proving that a server is allowed to send for your domain and that messages have not been altered. Our FAQ on SPF, DKIM and DMARC explains each.
- Bounce: a message returned because the address does not exist or the mailbox cannot accept it.
Why this matters in India
Shared hosting is a common weak point
Many Indian small-business websites run on low-cost shared hosting, which usually includes a built-in mail server. Because many unrelated sites share the same server and IP address, one spammer can damage everyone’s reputation, and messages from your contact form or store may land in spam. Routing through a dedicated relay such as Mailpro’s SMTP server avoids this.
Phishing makes filters strict
Indian inboxes receive a steady flow of phishing emails imitating banks, couriers, tax departments and payment apps. Mail providers respond with strict filtering, so unauthenticated messages from legitimate businesses can be caught too. Proper SPF, DKIM and DMARC records help separate your real invoices from fakes.
Personal data travels inside emails
Invoices, statements and reports contain personal data. The Digital Personal Data Protection Act 2023 expects reasonable security safeguards, and an encrypted connection (Mailpro uses TLS 1.3) is a basic one.
SMTP vs sending from Gmail
Sending business email from a personal Gmail account or a shared-hosting mailbox works for a few messages a day. It does not scale: providers limit daily volumes, you get no delivery statistics, and your personal account’s reputation is tied to your business sending. A professional relay gives you authentication, deliverability routing, statistics and higher volumes.
SMTP or API?
SMTP is the simplest option when you use existing software. If you are building an application, an API may give you more control. See API vs SMTP for a comparison.
Try it with Mailpro
Mailpro has provided email infrastructure since 2001 and hosts data in Switzerland, outside US jurisdiction. You can test the SMTP relay with 500 free credits, and pricing is based on emails sent.