SMTP
SMTP (Simple Mail Transfer Protocol) is a standard protocol that servers use to send email from sender to recipient.
Every time you press the send button on an email, SMTP works behind the scenes to deliver the message to the destination server.
Simple analogy
If email is a letter, then SMTP is the courier service. The task is one: pick up the letter from the sender and deliver it to the destination post office. Once it arrives, another protocol (IMAP or POP3) is responsible for storing and displaying the letter in the recipient's inbox.
How It Works
When you send an email, the process goes like this:
1. Email client (Gmail, Outlook, Thunderbird) contacts your SMTP server 2. The SMTP server verifies the identity of the sender
3. The SMTP server contacts the receiving SMTP server and hands over the email
- The recipient's server stores the email in the inbox — ready to be read via IMAP or POP3
SMTP only handles sending outgoing email. To receive and read e-mail, separate protocols are used: IMAP (two-way synchronization) or POP3 (download to local device).
Commonly Used SMTP Ports
| Ports | Encryption | Description |
|---|---|---|
| 25 | None | SMTP's native port, now generally blocked by ISPs to prevent spam |
| 465 | SSL/TLS | Old port for encrypted SMTP, still used by some providers |
| 587 | STARTTLS | Current recommended ports for authenticated email delivery |
| 2525 | STARTTLS | Alternative if port 587 is blocked |
If you set up the email client manually, use port 587 with STARTTLS as the primary option. This is the standard recommended by RFC 6409.
Own SMTP Server vs Third Party SMTP Service
Hosting with email packages usually includes a built-in SMTP server. However, for the needs of sending large volumes of email - such as newsletters or transactional notifications - hosting's built-in SMTP is often not reliable enough.
| Hosting Built-in SMTP | Third Party SMTP Services | |
|---|---|---|
| Price | Package included | Paid, depending on volume |
| Deliverability | Medium — depends on the reputation of the shared IP | Higher — IP with a maintained reputation |
| Volume | Limited | Can be very large |
| Suitable for | Daily business email | Newsletters, transactional emails Commonly used third-party SMTP services include Mailgun, SendGrid, Amazon SES, and Brevo. |
Why Do Emails Go to Spam? Relation to SMTP
SMTP itself does not guarantee that emails will reach your inbox. Email deliverability is greatly influenced by the supporting configurations that need to be set in your domain's DNS:
SPF — Defines which servers are allowed to send email on behalf of your domain
DKIM — Adds a digital signature to each email as proof of authenticity
DMARC — Instructs the receiving server on how to handle emails that fail SPF or DKIM
IP Reputation — The sending server IP is not blacklisted
Reverse DNS (PTR Record) — Server IP has a valid and appropriate hostname
verification
If your business email often ends up in the spam folder, check the SPF and DKIM configuration first. These two are the most common causes of deliverability problems. You can use tools like MXToolbox to diagnose this problem for free.
What You Need to Pay Attention to
- Don't use SMTP hosting to send mass emails — The risk of an IP being blacklisted is very high, and has an impact on all emails that go out from the same server, including other users' emails.
- Always use encryption — Make sure the connection to the SMTP server uses SSL/TLS or STARTTLS. Sending email without encryption makes the contents of the message vulnerable to being intercepted.
- Store SMTP credentials securely — Leaked SMTP usernames and passwords can be misused to send large amounts of spam on your domain name.
FAQs
Is SMTP the same as email hosting?
No. Email hosting is a service that provides a mailbox for your domain. SMTP is one of the protocols used in it — specifically for sending outgoing emails. Email hosting usually includes SMTP, IMAP, and a webmail interface at once.
How do I find my hosting's SMTP settings?
Usually available on your dashboard page or hosting documentation. The common format is mail.namadomain.com or smtp.namadomain.com. If not found, contact hosting support and ask for details of the SMTP outgoing server and the port used.
Does WordPress need special SMTP configuration?
Yes. By default WordPress uses PHP's built-in mail() function to send emails, which are often blocked or considered spam by the receiving server. It is recommended to use a plugin such as WP Mail SMTP and connect it to a proper SMTP server so that email notifications, password resets, and order confirmations are sent reliably.
What is the difference between SMTP and IMAP and POP3?
All three are email protocols but with different functions. SMTP to send outgoing email. IMAP for reading and syncing email across devices bi-directionally. POP3 to download emails to one local device — once downloaded, emails are deleted from the server.
Disclaimer: Hosting Wiki articles are prepared for educational and reference purposes. Hosting technology keeps evolving, so some technical details may change over time.