www.mailgun.com Open in urlscan Pro
2600:9000:2156:2200:b:b0de:6300:93a1  Public Scan

Form analysis
0 forms found in the DOM

Text Content

Auf dieser Website werden Daten wie Cookies gespeichert, um wichtige Funktionen
der Website sowie Marketing, Personalisierung und Analyse zu ermöglichen. Sie
können Ihre Einstellungen jederzeit ändern oder die Standardeinstellungen
übernehmen. Datenspeicherungsrichtlinie
Einstellungen verwalten Alle akzeptieren


This app works best with JavaScript enabled.

Menu

 * Pricing
 * Products
   
    * Email API
      
      Get set up in minutes and reach the inbox with confidence.
   
    * Deliverability Services
      
      Ensure every email lands where it's supposed to.
   
    * InboxReady
      
      Industry-leading tools to help you hit the inbox.
   
    * Email Verification
      
      Verify that an email address from your list actually exists.
   
    * Mailjet Email Marketing
      
      The email marketing solution for fast-moving teams
   
    * Inbox Placement
      
      Catch deliverability issues before they impact your business.

 * Deliverability Services
   
    * Deliverability Services
      
      Partner with an email expert to improve your deliverability.
   
    * Enterprise Services
      
      Grow an enterprise email program with deliverability in mind.

 * Solutions
   
    * Deliverability
      
      Land your emails in the inbox with deliverability features.
   
    * SMTP
      
      Get started in seconds with robust email delivery through SMTP.
   
    * Email Sending
      
      Personalize, schedule, and send all your emails with confidence.
   
    * Email Parsing
      
      Automatically parse incoming messages - no more manual work.
   
    * Email Marketing
      
      Engage with customers with the right campaign at the right time.
   
    * Transactional Email
      
      Trigger emails when a user takes a specific action in your app.
   
    * Send Time Optimization
      
      Send emails at the best time to engage with your audience.
   
    * Email Analytics
      
      Optimize your email performance with powerful analytics.
   
    * Burst Sending
      
      Attempted delivery of up to 15 million emails in a single hour,
      guaranteed.

 * Docs & Blog
   
    * Blog
      
      Read our lastest articles, product updates, and email tips.
   
    * Documentation
      
      Check out the full documentation and grab code samples.
   
    * Quickstart Guide
      
      Get up and running fast to start making the most of Mailgun.
   
    * Case Studies
      
      Learn from stories of other customers like you.
   
    * Podcasts
      
      A podcast about how we communicate with each other.
   
    * Videos
      
      See what Mailgun's all about, watch our webinars, and more
   
    * Guides
      
      Learn the ins and outs of email and sending best practices.
   
    * Help Center
      
      Get answers to common questions about Mailgun

 * Contact
   
    * Talk To Sales
      
      Talk to our Sales Team to see how we can increase your deliverability.
   
    * Get Help With Your Account
      
      Find answers to your support questions or technical issues.
   
    * Schedule A Demo
      
      Schedule a demo to see the Mailgun platform in action.

Log InGet Started
 * Featured Stories
 * Popular Stories
 * Categories
   
    * Best practices
      
      
   
    * Customer success
      
      
   
    * Email DIY
      
      
   
    * For devs
      
      
   
    * Quick tips
      
      
   
    * Security
      
      
   
    * What's new
      
      

 * Subscribe

Blog /Which SMTP Port Should I Use? Understanding Ports 25, 465, & 587
 * Email DIY


WHICH SMTP PORT SHOULD I USE? UNDERSTANDING PORTS 25, 465, & 587

Mailgun Team
• 5 min read


It's a common question that we receive here at Mailgun about SMTP port numbers.
To ensure connectivity to our Simple Mail Transfer Protocol (SMTP) endpoint,
Mailgun offers multiple SMTP port options, but which one should you use to send
email messages? We’ll take a historical look at each SMTP port and then we'll
discuss today's methodology for outgoing mail usage. If you're not a history
buff, go to "Which SMTP port should you use?" for the most common SMTP ports.


WHAT IS AN SMTP PORT?

Before our trip through history, we’ll clarify some basic definitions.

SMTP stands for Simple Mail Transfer Protocol—put simply, it’s the process by
which emails are sent across the Internet. Computer ports are how individual
computers connect to a network and complete electronic processes. An SMTP port
is a combination of both: a port designed to send email through a network and to
its recipient.

Of course, just as there are multiple computer ports, there are many SMTP ports
that can be used. Let’s take a look at their development.




SMTP PORTS: A HISTORICAL PERSPECTIVE

In 1982, the University of Southern California submitted a proposal to the
Internet Engineering Task Force (IETF). Request For Comments (RFC) 821 was
published, establishing port 25 as the default transmission channel for internet
email. 30 years later, we still use port 25 as the primary means of transmitting
email between two mail servers. A few RFCs have obsoleted the initial SMTP RFC.
However, the basis for SMTP connections remains the same or similar.

In December of 1998, R. Gellens and J. Klensin submitted RFC 2476 in support of
adding a new specification for internet email communications. The RFC proposed a
split of the traditional message submission and message relay concept. The RFC
defined that message submission should occur over port 587 to ensure new policy
and security requirements don't interfere with the traditional relay traffic
over message relay port 25.

DELIVERABILITY SERVICES

Learn about our Deliverability Services

Looking to send a high volume of emails? Our email experts can supercharge your
email performance. See how we've helped companies like Lyft, Shopify, Github
increase their email delivery rates to an average of 97%.


Learn More


WHAT ABOUT PORT 465?

Interestingly, port 465 was never published as an official SMTP transmission or
submission channel by the IETF. Instead, the Internet Assigned Numbers Authority
(IANA), who maintains much of the core internet infrastructure, registered port
465 for SMTPS. The purpose was to establish a port for SMTP to operate using
Secure Sockets Layer (SSL). SSL is commonly used for encrypting communications
over the internet.

The port was assigned for about one year when it was revoked in support of
securing SMTP communications using Transport Layer Security (TLS). The nail in
the coffin was a new protocol command "STARTTLS," introduced in RFC 2487. This
command allows SMTP servers to communicate over existing ports by advertising
whether the destination server supports TLS encryption. If so, the sending
server can upgrade the connection using the "STARTTLS" SMTP command.

Mailgun supports TLS connections, which you can verify by connecting and issuing
an "ehlo" from a command line interface. The resultant "250 STARTTLS" confirms
the endpoint accepts TLS connection requests.

1> telnet smtp.mailgun.org 587
2Trying 50.56.21.178...
3Connected to smtp.mailgun.org.
4Escape character is '^]'.
5220 ak47 ESMTP ready
6> ehlo blog.mailgun.com
7250-ak47
8250-AUTH PLAIN LOGIN
9250-SIZE 52428800
10250-8BITMIME
11250-ENHANCEDSTATUSCODES
12250 STARTTLS


You can test using the same command sequence on any SMTP server. Try Gmail or
Yahoo, "telnet gmail-smtp-in.l.google.com 25" or "telnet mta7.am0.yahoodns.net
25".


WHICH SMTP PORT SHOULD YOU USE?

What about today? How are these standard ports different? Have any deprecated
over time?


PORT 25:

SMTP port 25 continues to be used primarily for SMTP relaying. SMTP relaying is
the transmission of email from email server to email server.

In most cases, modern SMTP email clients (Microsoft Outlook, Mail, Thunderbird,
etc.) shouldn't use this port. It is traditionally blocked by residential ISPs
and Cloud Hosting Providers, to curb the amount of spam that is relayed from
compromised computers or servers. Unless you're specifically managing a mail
server, you should have no traffic traversing this port on your computer or
server. 


PORT 465:

IANA has reassigned a new service to this port, and it should no longer be used
for SMTP communications.

However, because it was once recognized by IANA as valid, there may be legacy
systems that are only capable of using this connection method. Typically, you
will use this port only if your application demands it. A quick Google search,
and you'll find many consumer Inbox Service Providers' (ISPs) articles that
suggest port 465 as the recommended setup. However, we do not recommend it, as
it is not RFC compliant.


PORT 2525:

This port is not endorsed by the IETF nor IANA. Instead, Mailgun provides it as
an alternate port, which mirrors port 587, in the event the above ports are
blocked. Because 2525 is a non-traditional high port number, it is typically
allowed on consumer ISPs and Cloud Hosting providers, like Google Compute
Engine. If you’ve tried the above ports, but experience connectivity issues, try
port 2525. This port also supports TLS encryption.


PORT 587:

This is the default mail submission port. When users submit an email to be
routed by a proper mail server, this is the one that will provide best results.

Port 587, coupled with TLS encryption, ensures that email is submitted securely
and following the guidelines set out by the IETF.

All Mailgun customers should consider using port 587 as their default SMTP port
unless you're explicitly blocked by your upstream network or hosting provider.


WAIT, WHAT ABOUT POP AND IMAP?

POP (Post Office Protocol, with the latest version being POP3) and IMAP
(Internet Message Access Protocol) are two of the very first protocols developed
on the consumer Internet that allowed for email clients - like Outlook,
Thunderbird and others - to retrieve mail from a mail server.

The ports typically used for POP are TCP ports 110 and 995, and for IMAP are TCP
ports 143 and 993, for insecure and secure sessions respectively. They were each
good at doing different things, like reflecting the state of an email back to
the server (whether it was read, flagged, or marked as junk), or for preserving
a copy of the message on a local machine for easy offline access.  The latest
version of POP, POP3, can be used with or without an SMTP.

This does not affect which port you can use with Mailgun. Mailgun doesn’t host
mailboxes, so these aren’t protocols we support.


USING SMTP WITH MAILGUN

SMTP has been around for years, and many folks ask us whether they should use
SMTP or Mailgun's API endpoint. Deciding whether you should use an email API or
SMTP to send your emails might not be an easy choice.

We certainly recognize there is some level of vendor lock-in associated with
building around an API. However, SMTP is extremely "chatty" and may lead to less
performant mail submission to Mailgun.

For example, consider the typical TLS mail conversation between my computer and
Mailgun's SMTP endpoint:

1> openssl s_client -starttls smtp -crlf -connect smtp.mailgun.org:587
2250 STARTTLS
3> ehlo blog.mailgun.com
4250-ak47
5250-AUTH PLAIN LOGIN
6250-SIZE 52428800
7250-8BITMIME
8250-ENHANCEDSTATUSCODES
9> AUTH PLAIN AHBvc3RtYXN0ZXJAc2FtcGxlcy5tYWlsZ3VuLm9yZwAza2g5dW11am9yYTU=
10235 2.0.0 OK
11> MAIL FROM:<test@samples.mailgun.org>
12250 Sender address accepted
13> RCPT TO:<recipient@samples.mailgun.org>
14250 Recipient address accepted
15> DATA
16354 Continue
17> This is a test of SMTP over port 587.
18> .
19250 Great success
20> QUIT
21221 See you later. Yours truly, Mailgun


As you can see, the above communication is quite cumbersome with lots of back
and forth between sender and receiver. We open a connection to the SMTP server,
issue the EHLO command, authenticate, set the MAIL FROM, set the RCPT TO, DATA
command, send the data, period to close, and finally receive confirmation the
message was queued.

Compare this with an HTTPs payload:

1> openssl s_client -connect api.mailgun.net:443
2> POST /v2/samples.mailgun.org/messages HTTP/1.1
3> Authorization: Basic YXBpOmtleS0zYXg2eG5qcDI5amQ2ZmRzNGdjMzczc2d2anh0ZW9sMA==
4> Content-Type: application/x-www-form-urlencoded
5> Content-Length: 126
6>
7>
from=test%40samples.mailgun.org&to=recipient%40samples.mailgun.org&subject=Testing&
8> text=This+is+a+test+of+HTTP+over+port+443!
9HTTP/1.1 200 OK


Here, we initiate a connection, pass the HTTP POST payload and receive a 200 OK
from the API endpoint. We don't have to issue a sequence of commands and wait
for a response from the server after each command.


WHAT SHOULD YOU REMEMBER ABOUT SMTP PORTS?

In summary, where performance is desired, Mailgun recommends utilizing our API
endpoint. The amount of back and forth “chatting” is much less. And with our API
SDKs, connecting up is pretty simple. If you’re not interested in connecting via
API, our SMTP endpoints are ready for your mail. Just don’t forget – port 587 is
where the party is at as far as secure SMTPs are concerned!

To learn more, check out our Documentation for more info, or contact us and we
can answer any questions you may have about SMTP ports or our email services.

DELIVERABILITY SERVICES

Learn about our Deliverability Services

Looking to send a high volume of emails? Our email experts can supercharge your
email performance. See how we've helped companies like Lyft, Shopify, Github
increase their email delivery rates to an average of 97%.


Learn More



Tags: SMTPSendingSMTP PortPOPIMAP

Last updated on September 20, 2021

 * Related posts
 * Recent posts
 * Top posts
   

View all
 *  * For devs
   
   How to Improve the Way WordPress Websites Send Email
   
   Konstantin Kovshenin
   • 7 min read
 *  * Email DIY
   
   The Difference Between SMTP and API
   
   Mary Dolan
   • 7 min read
 *  * Email DIY
   
   The Basics of Email Dark Mode
   
   Mary Dolan
   • 10 min read
 *  * Best Practices
   
   COVID-19 Survey: How the Pandemic Has Affected Email Sending
   
   Mary Dolan
   • 11 min read
 *  * Email DIY
   
   The Top Email Clients and Email Apps of 2021
   
   Mary Dolan
   • 12 min read
 *  * Email DIY
   
   The Benefits of Email Automation
   
   Mary Dolan
   • 8 min read
 *  * Best Practices
   
   How To Avoid Emails Going To Spam
   
   Jonathan Torres
   • 7 min read
 *  * Best Practices
   
   Preparing Your Email Infrastructure Correctly
   
   Kevin George
   • 8 min read
 *  * Best Practices
   
   When Should You Use An Email API?
   
   Mary Dolan
   • 5 min read
 *  * Best Practices
   
   The Best Time to Send Holiday Emails - Investigated
   
   Natalie Hays
   • 4 min read



 *  * For devs
   
   How to Improve the Way WordPress Websites Send Email
   
   Konstantin Kovshenin
   • 7 min read
 *  * What's new
   
   Email’s Not Dead Season 3 Is Finally Here
   
   Thomas Knierien
   • 3 min read
 *  * Quick tips
   
   How to Improve Holiday Supply Chain Communication with Email
   
   Kasey Steinbrinck
   • 9 min read
 *  * Best Practices
   
   How To Prepare Your Infrastructure For Black Friday
   
   James Tetler
   • 18 min read
 *  * Best Practices
   
   Happy Festivus: Email Deliverability Guide For The Holiday Season
   
   Kate Nowrouzi
   • 6 min read
 *  * Email DIY
   
   Dark Mode for Email Survey: What Do Email Senders Think?
   
   Kasey Steinbrinck
   • 10 min read
 *  * Email DIY
   
   Email Accessibility Mistakes that Annoy Subscribers & How To Fix Them
   
   Beatriz Redondo Tejedor
   • 13 min read
 *  * Security
   
   Vulnerability Management: Working With the Community To Patch Security
   Threats
   
   Jesse Kinser
   • 7 min read
 *  * What's new
   
   Celebramos el Mes de la Herencia Hispana
   
   Thomas Knierien
   • 7 min read
 *  * What's new
   
   Sinch to Acquire Mailgun, Creating a Best-Of-Breed Cloud Communications
   Platform
   
   William Conway
   • 4 min read



 *  * What's new
   
   Email’s Not Dead Season 3 Is Finally Here
   
   Thomas Knierien
   • 3 min read
 *  * Quick tips
   
   How to Improve Holiday Supply Chain Communication with Email
   
   Kasey Steinbrinck
   • 9 min read
 *  * Best Practices
   
   How To Prepare Your Infrastructure For Black Friday
   
   James Tetler
   • 18 min read
 *  * Best Practices
   
   Happy Festivus: Email Deliverability Guide For The Holiday Season
   
   Kate Nowrouzi
   • 6 min read
 *  * Email DIY
   
   Dark Mode for Email Survey: What Do Email Senders Think?
   
   Kasey Steinbrinck
   • 10 min read
 *  * Security
   
   Vulnerability Management: Working With the Community To Patch Security
   Threats
   
   Jesse Kinser
   • 7 min read
 *  * What's new
   
   Sinch to Acquire Mailgun, Creating a Best-Of-Breed Cloud Communications
   Platform
   
   William Conway
   • 4 min read
 *  * Best Practices
   
   The Future of Email: BIMI & AMP
   
   Kate Nowrouzi
   • 9 min read
 *  * Events
   
   Meet Our Amazing Pathwire Mavericks!
   
   Mary Dolan
   • 9 min read
 *  * What's new
   
   Continuing our commitment: HTTPS innovation and optimization
   
   Chris Farmer
   • 7 min read




Always be in the know and grab free email resources!

No spam, ever. Only musings and writings from the Mailgun team.



By sending this form, I agree that Mailgun may contact me and process my data in
accordance with its Privacy Policy.


sign up
It's easy to get started. And it's free.
See what you can accomplish with the world's best email delivery platform.

Sign up for Free

sales@mailgun.com
Company
AboutJobsContactReport spamSitemapCovid-19Mailjet
Why Mailgun?
Email for developersEmail service providerEmail consulting serviceWhite label
email service
Top Features
Email logsEmail analyticsSending EmailSMTP servicesEmail address validationEmail
list managementBounce management
Customers
Case studiesCustomersPartnersProduct status
Resources
BlogGuidesVideosPodcastsEventsMaverick ProgramDocumentationHelp centerSend us
your feedbackEmail Growth Playbook
More about email
Mass emailEmail reputationIP reputationBlacklist monitoringEmail templatesEmail
testing toolsEmail spam checkerEmail GlossaryEmail Marketing ROI Calculator

©2021 Mailgun Technologies, Inc. All Rights Reserved.

Cookie PreferencesGDPR ComplianceAcceptable Use PolicyTerms of ServicePrivacy
Policy