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Welcome to smtp.codes

We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.

Contribute

Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!

If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.

Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes

Deployment

A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.

Issues & Comments

Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes

License

smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.

Acknowledgements

We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.

About

A collection of SMTP responses from email systems and what they mean.

smtp.codes

Topics

emailsmtp

Resources

Readme
MIT license

Contributing

Contributing
Activity

Stars

11 stars

Watchers

4 watching

Forks

7 forks
Report repository

Contributors

Languages

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(function(){
try {
var __m = "github.com";
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Skip to content
BranchesTags
Repository files navigation
Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
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Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
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Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
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})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
BranchesTags
Repository files navigation
Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
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function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
BranchesTags
Repository files navigation
Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
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applyDarkMode();
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});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
BranchesTags
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Welcome to smtp.codes
We created this guide to help you understand what the SMTP codes that various email servers respond with. This is super useful when troubleshooting email delivery and a tool every email marketer, deliverability person or email engineer should have in their tool kit.
Contribute
Ran into an SMTP code that wasn't very helpful and you figured out what it means? or maybe you work for an email provicer and want to contribute the codes your services returns so you can decrease your support volume? We'd love to help you document them!
If you plan on making additions or edits to existing SMTP responses, you’ll need to fork the repo and submit a pull request. All of the data is stored as JSON in the /data folder. We recommend you run your changes through a JSON linter before commiting.
Feel free to file an issue if you don’t feel like dealing with code. If you do not have a GitHub account, you can also submit them via email at submit@smtp.codes
Deployment
A homegrown build script builds the website via an Action and then publishes it to GitHub Pages.
Issues & Comments
Feel free to contact us if you encounter any issues. Please leave all comments, bugs, requests and issues on the Issues page. If you do not have a GitHub account, you are welcome to send your feedback via email to feedback@smtp.codes
License
smtp.codes is licensed under the MIT license. Please refer to the LICENSE for more information.
Acknowledgements
We'd like to thank the ActiveCampaign Postmark team for spear-heading the initiative with SMTP Field Manual, from where we based the initial scope for this project.
About
A collection of SMTP responses from email systems and what they mean.
smtp.codes
Topics
emailsmtp
Resources
Readme
MIT license
Contributing
Contributing
Activity
Stars
11 stars
Watchers
4 watching
Forks
7 forks
Report repository
Contributors
Languages