What Is an SMTP Server?
Warren DuffSMTP servers are complicated, and if you’re just dipping your toe into the how-email-gets-sent world, it’s easy to feel overwhelmed. To help you navigate your email sending—specifically, an SMTP server to send email—we’ve put together a list of the most common SMTP server questions we receive, so you’ll be an SMTP expert in no time.
What is an SMTP server?
What does SMTP mean? We’re glad you asked. SMTP stands for Simple Mail Transfer Protocol, and it’s an application used by mail servers to send, receive, and/or relay outgoing mail between email senders and receivers.
An SMTP email server will have an address (or addresses) that the mail client or application you use can set and generally looks like this: smtp.serveraddress.com. For example, the SMTP server Gmail uses is smtp.gmail.com, and Twilio SendGrid’s is smtp.sendgrid.com. You can generally find your SMTP email server address in the account or settings section of your mail client.
When you send an email, with SMTP host Gmail or AOL, the SMTP server processes your email, decides which server to send the message to, and relays the message to that server. The recipient’s inbox service provider, such as Gmail or AOL, then downloads the message and places it in the recipient’s inbox.
You can find more details on SMTP servers on our docs page.
Is an SMTP server the same as a normal server?
Technically, yes. Like most servers, the SMTP server processes data to send to another server, but it has the very specific purpose of processing data related to the sending, receiving, and relaying of email. An SMTP server is also not necessarily on a machine. It’s an application constantly running in anticipation of sending new mail.
Why are SMTP servers important?
Without an SMTP server, your email wouldn’t make it to its destination. Once you hit Send, your email transforms into a string of code sent to the SMTP server. The SMTP server processes that code and passes on the message. If the SMTP server wasn’t there to process the message, it would be lost in translation.
Additionally, the SMTP server verifies that the outgoing email is from an active account, acting as the first safeguard in protecting your inbox from illegitimate email. It also will send the email back to the SMTP sender if it’s undeliverable. This informs the sender that they have the wrong email address or that the receiving server has blocked the email.
If you’re looking for more information on SMTP, check out our post, SMTP Service Crash Course.
Common SMTP server providers & settings
| SMTP Provider | URL | SMTP Settings |
| AOL | aol.com | smtp.aol.com |
| AT&T | att.net | smtp.mail.att.net |
| Comcast | comcast.net | smtp.comcast.net |
| iCloud | icloud.com/mail | smtp.mail.me.com |
| Gmail | gmail.com | smtp.gmail.com |
| Outlook | outlook.com | smtp-mail.outlook.com |
| Yahoo! | mail.yahoo.com | smtp.mail.yahoo.com |
How the Twilio SendGrid SMTP server works
What does the SMTP server do when I send email with Twilio SendGrid?
- Your mail client connects to the SendGrid SMTP server, smtp.sendgrid.net, using port 25 (by default).
- Your mail client has a conversation with our server, first verifying that the username and password used for authentication correspond to an active account, then relaying the message information, such as sender address, recipient, and message content.
- Our server takes the message information we gathered from your request and then repeats the conversation process in Step 2 with the recipient’s mail server.
- Your recipient’s mail server checks the sending address, recipient address (to ensure they are a valid recipient), and message content. It checks the sending domain for any potential DNS issues, such as invalid DKIM and SPF signatures. As long as there are no issues, the recipient’s mail server will use the protocols POP3 or IMAP to retrieve the email and deliver the message to its intended recipient.
Take a look at the diagram below for a visual of the SMTP email delivery process.
Does Twilio SendGrid have a test SMTP server?
SendGrid offers free accounts that don’t require a credit card to enable. With a free SendGrid account, we give you access to the SendGrid SMTP server and allow you to send up to 100 emails/day—this effectively gives you an SMTP server for testing.
Active free account customers can use their account to send test messages and test their email deliverability before upgrading and sending larger amounts of email.
Do I need to set up the Twilio SendGrid SMTP server before sending email?
Nope! You just need to have an active SendGrid account and the ability to use basic username and password authentication within your email client or application.
What SMTP server port do I need to connect to?
We support unencrypted and TLS encryption on ports 25, 587, and 2525. If you’d like to implement SSL encryption, then use port 465.
Send an SMTP email with Twilio SendGrid
Ready to get sending with Twilio SendGrid? Check out our documentation to learn how to send an SMTP email. We’ll walk you step by step through getting started and link out to other helpful resources.
Sign up for a free account to get started. Or, if you already have an account but would like assistance, contact SendGrid support today!
