SMTP (Simple Mail Transfer Protocol) is a protocol or a set of rules that email clients use to exchange information. It sends your emails to the recipients. So after you hit \u2018Send,\u2019 the protocol pushes your message to the SMTP servers of your email client. Then, it goes to your recipient\u2019s mail server. The SMTP servers receive and deliver it to the recipient\u2019s inbox. <\/p>\n\n\n\n
SMTP is the first email protocol on an email\u2019s journey from a sender to a recipient. It\u2019s the only protocol for sending messages. There are also IMAP and POP3 email protocols. These are for receiving messages. We\u2019ll discuss them in detail later.<\/p>\n\n\n\n
Using an SMTP allows for authenticating your email address. A verified email address, in turn, brings benefits like:<\/p>\n\n\n\n
- \n
- higher email deliverability<\/li>\n\n\n\n
- safe bulk emails & campaigns<\/li>\n\n\n\n
- easy campaign data collection and reporting<\/li>\n<\/ul>\n\n\n\n
What is an SMTP mail server?<\/h2>\n\n\n\n
An SMTP server is an application that uses the protocol to send your emails. It pushes the messages from your device to the SMTP servers of your recipient\u2019s email client. It sounds like many steps for an email to go through, but the entire journey takes just a few moments.<\/p>\n\n\n\n
A good way to understand an SMTP server is by looking at email messages as sending out a used clothing item you\u2019ve just sold on eBay. Let\u2019s say you\u2019re selling a pair of vintage sneakers. You see someone has bought them, so you pack the contents in a box (type the mail message). You then fill in the recipient\u2019s address (like you\u2019d type in their email address). You print it out and bring it to a delivery service (hit \u2018Send\u2019). <\/p>\n\n\n\n
So what does an SMTP server mean in this example? Your local delivery service office is like an SMTP server. They check if the address is valid and the package matches the criteria. They follow a protocol to accept the package like the SMTP servers accept your email. Then, you go home (log out of your email client) and wait for the service to deliver your package. <\/p>\n\n\n\n
If everything\u2019s okay with the package, the service takes care of the delivery. They send your box to the recipient\u2019s city (recipient\u2019s email client\u2019s server). The city\u2019s delivery office follows the protocol for incoming packages to accept it (similarly to IMAP and POP3). If all rules have been followed, the person receives a delivery. This is when the recipient receives incoming messages from you.<\/p>\n\n\n\n
![\"delivery](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/delivery-of-emails-through-the-smtp-server.png\")
<\/figure>\n\n\n\n<\/span>How does SMTP work?<\/span><\/h2>\n\n\n\n
When you hit the \u2018Send\u2019 button on your email message, your mail user agent (MUA) connects to the SMTP server. An MUA is your email client, like Gmail or Yahoo. The connection is usually established via port 25. Check out our guide on how to send emails with Gmail SMTP<\/a>.<\/p>\n\n\n\n
So your mail client introduces itself to the SMTP server with a command. The MUA\u2019s introduction, followed by the SMTP server\u2019s reply, is called an SMTP server handshake. <\/p>\n\n\n\n
Next, the Message Transfer Agent, or Mail Transfer Agent (MTA), sees the email client you\u2019re using to send your mail message. If it\u2019s the same as the recipient\u2019s one, the MTA pushes the message to the recipient\u2019s inbound SMTP servers right away. If the mail client is different, the MTA identifies the client via the Domain Name System (DNS). It then sends it to the right server. The message is queued or sent to a backup server if SMTP servers are unavailable.<\/p>\n\n\n\n
Your recipient\u2019s email client finally gets the message. The server sends it to the person\u2019s inbox, where they can access it.<\/p>\n\n\n\n
![\"movement](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/movement-of-emails-from-the-mail-user-agent-to-the-smtp-server.png\")
Source<\/em><\/a><\/figcaption><\/figure>\n\n\n\n Basic SMTP Commands<\/h3>\n\n\n\n
An SMTP server command is text-based and is limited to 510 characters each. And what does the SMTP server do? It replies to the command with a numerical code. There are many SMTP commands the SMTP relay servers use to communicate with other servers. Here are the most used ones listed in the order they come in an SMTP relay servers conversation.<\/p>\n\n\n\n
HELO<\/h4>\n\n\n\n
HELO is the first command that starts the conversation. It introduces the IP address or the domain of the email client to the SMTP server. If the server responds, this interaction is what we mentioned earlier as a handshake.<\/p>\n\n\n\n
Example:
Client<\/strong>: HELO client.com
Server<\/strong>: 250 client.com<\/p>\n\n\n\nEHLO<\/h4>\n\n\n\n
The EHLO command performs the same action as HELO. But only servers supporting the SMTP server service extensions recognize it. Otherwise, the server replies with an error.<\/p>\n\n\n\n
Example:
Client<\/strong>: EHLO client.com
Server<\/strong>: 250 client.com<\/p>\n\n\n\nMAIL FROM<\/h4>\n\n\n\n
MAIL FROM starts the email transfer process \u2014 it introduces the sender’s email address. The server receives the address and checks the email client’s domain. If it\u2019s valid and acceptable, it replies to confirm that it can move to the next step.<\/p>\n\n\n\n
Example:
Mail Client<\/strong>: MAIL FROM sender@client.com
Server<\/strong>: 250 OK<\/p>\n\n\n\nRCPT TO<\/h4>\n\n\n\n
RCPT TO does the same as MAIL FROM but for the recipient. The command requests to confirm that the email address can receive the email. In case there are several recipients, the command repeats for each address.<\/p>\n\n\n\n
Example:
Client<\/strong>: RCPT TO recipient@client.com
Server<\/strong>: 250 OK<\/p>\n\n\n\n![\"rcpt](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/rcpt-to-command-in-the-smtp-server.png\")
S<\/em><\/a>ource<\/a><\/em><\/figcaption><\/figure>\n\n\n\n DATA<\/h4>\n\n\n\n
DATA identifies the message body of the email as the data that the email client needs to transfer. The SMTP server has to confirm the transmission with the 354 code. Only then the actual message transmission begins. The client marks the end of the outgoing messages with a full stop.<\/p>\n\n\n\n
Example:
Client<\/strong>: DATA
Server<\/strong>: 354<\/p>\n\n\n\nClient<\/strong>: Date: 27 Apr 2022, 7:23:23 PM
From: sender@client.com
Subject: Example Subject Line
To: recipient@client.com
Body Text: Hey, This is an example email body text. Bye!
.<\/p>\n\n\n\nQUIT<\/h4>\n\n\n\n
The QUIT command ends the conversation between the email client and the SMTP server. To start the conversation again, the client has to send the HELO or EHLO commands.<\/p>\n\n\n\n
Example:
Client<\/strong>: QUIT
Server<\/strong>: 221 OK<\/p>\n\n\n\nThese are the essential SMTP server commands. But there are also additional ones like NOOP, HELP, EXPN, RSET, AUTH, ATRN, and others.<\/p>\n\n\n\n
Understanding SMTP error codes<\/h3>\n\n\n\n
The SMTP server replies with an error code to show that an issue has occurred. The error codes point to issues like the recipient\u2019s address doesn\u2019t exist in the database. Or the sender email has sent spam before. Error codes in SMTP relay conversations start with a 4<\/strong> or 5<\/strong>.<\/p>\n\n\n\n
4.X.X error codes<\/h4>\n\n\n\n
Temporary errors start with a 4, meaning that they will be fixed soon and you can try again later. These are the temporary SMTP server error codes you can come across:<\/p>\n\n\n\n
- \n
- 421 \u2014 server is unavailable at the moment<\/li>\n\n\n\n
- 450 \u2014 the encountered mail server is unavailable at the moment<\/li>\n\n\n\n
- 451 \u2014 the server error caused a failure when sending the message<\/li>\n\n\n\n
- 452 \u2014 the server storage is full, the command has stopped<\/li>\n\n\n\n
- 455 \u2014 the server can’t reply to the command for other reasons<\/li>\n<\/ul>\n\n\n\n
5.X.X error codes<\/h4>\n\n\n\n
Error codes for permanent failures start with a 5 and need action to be fixed. Here are the permanent issue codes to know:<\/p>\n\n\n\n
- \n
- 500 \u2014 the command contains a syntax error, the server can’t recognize it<\/li>\n\n\n\n
- 501 \u2014 the server doesn\u2019t recognize the command because of a syntax error<\/li>\n\n\n\n
- 502 \u2014 the command is valid, but the server can’t perform it since it doesn’t support it<\/li>\n\n\n\n
- 503 \u2014 the client has sent the commands in a wrong order<\/li>\n\n\n\n
- 541 \u2014 the recipient’s address is blacklisted or has rejected the message because it violates email policy<\/li>\n\n\n\n
- 550 \u2014 the receiving server identifies the recipient’s address as unavailable<\/li>\n<\/ul>\n\n\n\n
![\"smtp](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/smtp-server-permanent-error-codes.png\")
<\/figure>\n\n\n\n- \n
- 551 \u2014 the sending server requires authentication or the recipient’s address is unavailable for the sender<\/li>\n\n\n\n
- 552 \u2014 the recipient’s inbox is full, it can’t receive the message<\/li>\n\n\n\n
- 553 \u2014 the recipient’s address doesn’t exist, or you spelled it wrong<\/li>\n\n\n\n
- 554 \u2014 transaction stopped and failed, no details are available<\/li>\n<\/ul>\n\n\n\n
How is SMTP different from other email protocols?<\/h2>\n\n\n\n
Email protocols are methods that establish a connection between servers. They use the connection to transfer an email. So an email travels from the sender\u2019s computer to the email client\u2019s server. It then goes to the destination server. The server stores the email for the recipient to access. Or they download the message to their device.<\/p>\n\n\n\n
Email protocols differ depending on how they establish the connection between servers. The protocols also differ in how they allow users to access their emails. There are 2 types of email protocols, inbound and outbound:<\/p>\n\n\n\n
- \n
- Inbound<\/strong> email protocols allow users to receive and access their emails. POP3 and IMAP are the most popular email protocols of this type. <\/li>\n\n\n\n
- Outbound <\/strong>email protocols, in turn, relay a message from the sender to the recipient. SMTP relay is an outbound email protocol.<\/li>\n<\/ul>\n\n\n\n
These <\/strong>are further divided into SMTP, POP, and IMAP<\/a> email protocols. The SMTP is the first protocol used on the journey of an email from a sender to a recipient. <\/p>\n\n\n\n
After the email reaches the server, its next step is the IMAP or POP3 protocol. IMAP allows receiving an email and accessing it from various devices. POP3 allows receiving an email and downloading it from the server to access it offline at any time.<\/p>\n\n\n\n
![\"pop3](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/pop3-vs-imap-email-protocols.jpg\")
Source<\/em><\/a><\/figcaption><\/figure>\n\n\n\n You can choose which email protocol to use for your email client. Since SMTP is the only outbound email protocol, there\u2019s no other choice for you. But it will ensure safe and worry-free marketing campaigns with transactional emails. This protocol also allows simple data collection and reporting on the campaigns. The data storage is centralized so all team members can access it.<\/p>\n\n\n\n
But as for IMAP and POP3, when should you choose which? Go for the one that meets your needs most:<\/p>\n\n\n\n
\n\nIMAP<\/strong><\/p>\n\n\n\n
- \n
- centralized storage \u2014 access to the mail server from any device or location<\/li>\n\n\n\n
- best for teams with several people<\/li>\n\n\n\n
- higher speed<\/li>\n<\/ul>\n<\/div>\n\n\n\n\n
POP3<\/strong><\/p>\n\n\n\n
- \n
- offline access to emails for unstable Internet connection<\/li>\n\n\n\n
- best for individuals<\/li>\n\n\n\n
- uses less email servers space<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Running your SMTP server vs. Using a third-party email service: What\u2019s best?<\/span><\/h2>\n\n\n\n
Emails are a great addition to any marketing strategy, so we must manage them well. You have to choose between hosting your SMTP server address and using the service of an SMTP provider<\/a> or a free SMTP server<\/a>. Both options have their benefits, but there are some drawbacks to each, too. Let\u2019s discuss what to expect.<\/p>\n\n\n\n
Hosting your SMTP server<\/h3>\n\n\n\n
Running your mail server means you have fewer limits. It gives you complete control over the privacy and security of your mail. But this is both a good and bad thing. You also have to know how to ensure security and troubleshoot problems.<\/p>\n\n\n\n
\n\nPros:<\/strong><\/p>\n\n\n\n
- \n
- You choose virus and spam protection software<\/li>\n\n\n\n
- Full control of outgoing email servers\u2019 privacy<\/li>\n\n\n\n
- No storage fees<\/li>\n\n\n\n
- No email volume limits<\/li>\n\n\n\n
- Hosting multiple domains<\/li>\n\n\n\n
- Non-shared IP address<\/li>\n\n\n\n
- Great customization possibilities<\/li>\n<\/ul>\n<\/div>\n\n\n\n\n
Cons:<\/strong><\/p>\n\n\n\n
- \n
- Quite difficult to get the hang of it<\/li>\n\n\n\n
- The saved money goes to updating security software<\/li>\n\n\n\n
- Email backups are your responsibility<\/li>\n\n\n\n
- You have to store the backup data in a different location<\/li>\n\n\n\n
- Higher bounce rates and chances to get blacklisted<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n\n\n
Using a third-party email provider<\/h3>\n\n\n\n
Unless you get everything you need from a free plan, you most likely have to pay for the mail server service.<\/p>\n\n\n\n
Email providers<\/a> are usually good at keeping their servers running at all times. Most services have their support teams available round the clock. So you get quite a handful of benefits when trusting your mail to an SMTP service provider.<\/p>\n\n\n\n
\n\nPros:<\/strong><\/p>\n\n\n\n
- \n
- Lots of software providers to choose from<\/li>\n\n\n\n
- Various subscription plans \u2014 only pay for what you need<\/li>\n\n\n\n
- Fast, professional troubleshooting and 24\/7 support<\/li>\n\n\n\n
- Secure email backups in multiple locations<\/li>\n\n\n\n
- Timely virus protection and spam software updates<\/li>\n\n\n\n
- No need to spend time figuring out how everything works<\/li>\n\n\n\n
- Trustworthy sender\u2019s reputation and low bounce rates<\/li>\n<\/ul>\n<\/div>\n\n\n\n\n
Cons:<\/strong><\/p>\n\n\n\n
- \n
- Fully relying on the service to troubleshoot issues<\/li>\n\n\n\n
- No control of data protection<\/li>\n\n\n\n
- Limited customization<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n\n\n
<\/span>5 <\/strong>Best SMTP Server Providers<\/span><\/h2>\n\n\n\n
There are many STMP services to set up an SMTP server. We collected the best free SMTP servers<\/a>, which also offer upgraded plans if you need more features. But here\u2019s a shortlist for convenience.<\/p>\n\n\n\n
<\/span>1. Brevo<\/span><\/h2>\n\n\n\n
![\"Brevo](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/Brevo-email-marketing-tool-with-smtp-server.png\")
<\/figure>\n\n\n\nBrevo<\/a> is one of the most popular email marketing tools. It also includes an SMTP server to send email campaigns and transactional emails.<\/p>\n\n\n\n
Along with an automation workflow builder, landing pages, forms, drag-and-drop editors, SMS marketing, live chat, and ads. Read our full Brevo review<\/a> to learn more about how these features work.<\/p>\n\n\n\n
Some free features in Brevo are APIs, real-time email statistics, templates, and advanced segmentation. The free plan limits you to 300 emails daily. <\/p>\n\n\n\n
Transactional emails start from $15\/month for 20K emails. There are 3 subscription plans in Brevo<\/a> for the marketing platform, too. Starter prices kick in at $9\/month for 5K emails. Business, starting at $18 monthly for 5K emails with marketing automation, ads, landing pages, and multi-user access. And Enterprise with custom pricing and a dedicated account manager.<\/p>\n\n\n\n
Get started with Brevo today<\/a><\/p>\n\n\n\n
<\/span>2. SMTP2GO<\/span><\/h2>\n\n\n\n
![\"smtp2go](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/smtp2go-email-delivery-service.png\")
<\/figure>\n\n\n\nSMTP2GO<\/a> is a reputable email delivery service. It has all the tools to properly set up and manage your outgoing emails. Your email delivery is uninterrupted even during an internet breakdown because of its redundant multi-data center infrastructure.<\/p>\n\n\n\n
SMTP2GO has an easy-to-use API, advanced email testing options, and actionable real-time reports. Validate your email with DKIM and SPF. Check how your emails display in 40+ email clients. You can track metrics like bounce rate, open rate, click rate, and unsubscribe rate.<\/p>\n\n\n\n
Try SMTP2GO for free<\/a> and get 1000 emails monthly and 5 days of advanced reporting. The Starter plan costs $10\/month<\/a> for 10K emails, SMS messaging, 30 days of reporting, subaccounts, ticket, chat, and phone support.<\/p>\n\n\n\n
Try SMTP2GO for free here<\/a><\/p>\n\n\n\n
<\/span>3. MailerSend<\/span><\/h2>\n\n\n\n
![\"Mailersend](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/Mailersend-transactional-email-service-and-safe-email-delivery.png\")
<\/figure>\n\n\n\nMailerSend<\/a> is a transactional email service with a drag-and-drop editor from the makers of MailerLite<\/a>. If you\u2019re considering a full email marketing platform, read our complete Mailerlite review<\/a>. It delivers your transactional emails safely, helping to improve your delivery rate. <\/p>\n\n\n\n
MailerSend offers email verification, transactional SMS, interaction tracking, campaign analytics, push updates, automation, and 10 integrations.<\/p>\n\n\n\n
![\"smtp](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/smtp-server-feature-in-Mailersend.png\")
<\/figure>\n\n\n\nSign up for free<\/a> and get 500 emails monthly. 1000 extra emails cost only $1.20. MailerSend pricing<\/a> starts at $7\/month for 5000 emails, 100 email verifications, and email support.<\/p>\n\n\n\n
Try MailerSend for free here<\/a><\/p>\n\n\n\n
<\/span>4. SMTP.com<\/span><\/h2>\n\n\n\n
![\"smtp.com](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/smtp.com-homepage.png\")
<\/figure>\n\n\n\nSMTP.com<\/a> is a specialized SMTP email relay service for marketing and transactional emails. They\u2019ve been in business for 20+ years serving 100K+ companies.<\/p>\n\n\n\n
The tool has secure authentication, reporting, features to protect your sender reputation, expert support, and 12 integrations.<\/p>\n\n\n\n
SMTP.com pricing starts at $25\/month for 50K emails, email relay API, detailed reporting, shared IP, email and phone support. 100K emails with a dedicated IP cost $80\/month.<\/p>\n\n\n\n
Sign up for SMTP.com here<\/a><\/p>\n\n\n\n
<\/span>5. Mailtrap<\/span><\/h2>\n\n\n\n
![\"mailtrap](\"https:\/\/www.emailvendorselection.com\/wp-content\/uploads\/mailtrap-smtp-email-api-provider-delivery-platform.png\")
<\/figure>\n\n\n\nMailtrap<\/a> is an email delivery platform to test, send, and control your email infrastructure. Send emails with Mailtrap\u2019s Email API or SMTP service. And if you want to make sure there aren’t any bugs in your emails before sending, you can inspect them with Mailtrap\u2019s Email Testing. It also comes with monitoring to control how your email infrastructure works and troubleshoot unexpected sending issues. <\/p>\n\n\n\n
Mailtrap has free plans for both Email API\/SMTP and Email Testing. Paid plans for Email API\/SMTP start at $15\/month for 10K emails.<\/p>\n\n\n\n
Get started with Mailtrap for free<\/a> or read our full review<\/a><\/p>\n\n\n\n
<\/span>Wrapping Up: What is SMTP<\/span><\/h2>\n\n\n\n
Let\u2019s recap what an SMTP server is. SMTP stands for Simple Mail Transfer Protocol. The protocol is a set of rules that email clients use to send your emails. SMTP server is an outbound email protocol. Some other email protocols are IMAP and POP3. These are inbound email protocols. <\/p>\n\n\n\n
SMTP servers use commands to communicate with inbound servers. They use error codes to notify of issues. 4.X.X errors are temporary, and 5.X.X won\u2019t resolve without action.<\/p>\n\n\n\n
It\u2019s best to rely on free SMTP services<\/a> for setup if you\u2019re a beginner with low volume. You get more features, quick responses for troubleshooting, and centralized data storage. Some of the best SMTP server providers are Brevo<\/a>, MailerSend<\/a>, and SMTP2GO<\/a>.<\/p>\n\n\n\n
SMTP servers, email verification tools<\/a>, and email testing tools<\/a> help reduce bounce rates, improve your sender\u2019s reputation, and increase your email delivery rate.<\/p>\n","protected":false},"excerpt":{"rendered":"
Without SMTP sending emails is impossible. We use it everyday, but don’t know what it is. Learn what is SMTP and how it works, why it matters in email marketing, and why you need a good SMTP server.<\/p>\n","protected":false},"author":177,"featured_media":64746,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_editorskit_title_hidden":false,"_editorskit_reading_time":11,"_editorskit_is_block_options_detached":false,"_editorskit_block_options_position":"{}","footnotes":""},"categories":[2],"tags":[],"dealstore":[],"coauthors":[848],"acf":[],"_links":{"self":[{"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/posts\/64694"}],"collection":[{"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/users\/177"}],"replies":[{"embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/comments?post=64694"}],"version-history":[{"count":20,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/posts\/64694\/revisions"}],"predecessor-version":[{"id":94081,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/posts\/64694\/revisions\/94081"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/media\/64746"}],"wp:attachment":[{"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/media?parent=64694"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/categories?post=64694"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/tags?post=64694"},{"taxonomy":"dealstore","embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/dealstore?post=64694"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.emailvendorselection.com\/wp-json\/wp\/v2\/coauthors?post=64694"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
- Outbound <\/strong>email protocols, in turn, relay a message from the sender to the recipient. SMTP relay is an outbound email protocol.<\/li>\n<\/ul>\n\n\n\n
- Inbound<\/strong> email protocols allow users to receive and access their emails. POP3 and IMAP are the most popular email protocols of this type. <\/li>\n\n\n\n