You just installed Discourse via the install guide, but email doesn’t seem to work. Unfortunately this means you can’t log in as an admin to finalize the install. 
Let’s troubleshootize!
Try the doctor 
If you run ./discourse-doctor it will check several ways that your mail configuration might be broken, and offer advice. Try that first.
Did you enter email settings correctly?
The simplest way is to run ./discourse-setup again. Did you enter everything correctly?
You can also double check the settings in your containers/app.yml file. A valid email section looks like this:
DISCOURSE_DEVELOPER_EMAILS: 'name@example.com'
DISCOURSE_SMTP_ADDRESS: smtp.mailgun.org
DISCOURSE_SMTP_PORT: 587
DISCOURSE_SMTP_USER_NAME: postmaster@discourse.example.com
DISCOURSE_SMTP_PASSWORD: aUd34cdWKCu6CTjfoH7ykk
Closely examine all values for correctness. Note that it all aligns, there are no leading # characters, and there are single quotes around the developer email field.
If you had any errors in your app.yml and made changes , you MUST rebuild the container for those changes to take effect!
cd /var/discourse/
./launcher rebuild app
Well, you don’t always need to rebuild
Doing a rebuild will often fix things that seem broken, but it takes a while. There are times when a full rebuild is not necessary; the above is usually the best advice, but If you change just SMTP settings, you can do just this to apply them without doing a full rebuild:
cd /var/discourse
./launcher destroy app
./launcher start app
Are your SMTP connections being blocked?
To confirm that your server can indeed contact the email server, issue this command:
telnet smtp.mailgun.org 587
If you can’t connect this way, you’re almost certainly blocked. (And if you do get connected, the escape character for SMTP is ctrl+], then use quit to exit telnet.)
If this happens, first try port 2525, and if that fails, contact your cloud provider support and confirm that your email connections are not being blocked.
What do the Discourse logs say?
From the command line, issue this command:
cd /var/discourse
tail shared/standalone/log/rails/production.log
This will show the last few lines of the log. Look for anything mail related. If you need to view the fuller logs, try
more shared/standalone/log/rails/production.log
To page through the complete log by pressing space. Look closely for any email related messages.
What do your email provider logs say?
Assuming there are no errors in the Discourse logs, or your Discourse mail configuration, the emails probably went out. The question, is what did your email provider do with them?
Most email providers have a log viewing function. Check the logs for your email domain and see what happened with the incoming emails.
Did you properly set up DKIM and SPF records for your domain?
You must enter those crucial DNS records for DKIM and SPF, otherwise your emails may arrive only sporadically, if at all.
Is the email domain correct?
The default email from address is based on the install domain plus subdomain, so if your URL is discourse.example.com it will be:
noreply@discourse.example.com
But if your mail provider is expecting:
noreply@example.com
… you may have problems! To get around this, edit and uncomment this line in app.yml
## If you want to set the 'From' email address for your first registration, uncomment and change:
#- exec: rails r "SiteSetting.notification_email='noreply@example.com'"
## After getting the first signup email, re-comment the line. It only needs to run once.
You’ll need to issue a rebuild after uncommenting the above line and setting the from email address as required.
You can also change this from the command line, if needed:
./launcher enter app
rails r "SiteSetting.notification_email = 'discourse@yoursite.com'"
exit
If using Mailgun – have you activated your domain and provided credit card info?
If you are using Mailgun, after you enter your DKIM and SPF records, you must visit https://mailgun.com/app/domains/YOUR.DISCOURSE.DOMAIN.com and click the “Check DNS Records Now” button. At the top of that page you should see “State ACTIVE” (in a calming green). If it says “State Unverified” (in a scary warning-yellow) Mailgun will not accept mail.
Mailgun now requires a credit card in order to deliver mail (other than to you). If your mailgun logs have a message about “free accounts,” this is your problem.
Other mail services have similar requirements.
Are you using an IP address as the mail domain?
This does not work in our experience. You must use a domain name when sending email, not an IP address like 192.168.1.1.
If you really want to go on with an IP address, try mail settings similar to these:
DISCOURSE_SMTP_ADDRESS: 172.17.0.1 # e.g. use internal docker IP here
DISCOURSE_SMTP_PORT: 587
DISCOURSE_SMTP_USER_NAME: "YOUR-SMTP-USER-NAME"
DISCOURSE_SMTP_PASSWORD: "YOUR-SMTP-PASSWORD"
DISCOURSE_SMTP_ENABLE_START_TLS: true # (optional, default true)
DISCOURSE_SMTP_OPENSSL_VERIFY_MODE: none
DISCOURSE_SMTP_DOMAIN: example.com
Need to log in without receiving a registration email?
We don’t recommend this, because your email is still broken, and you have a broken Discourse until email is working. But if you absolutely must log in as admin with email broken, here’s what to do:
cd /var/discourse
./launcher enter app
rake admin:create
And answer the prompts. It takes a few seconds before they appear. When it asks for the password, you will not be able to see what you type. That is why it makes you type it twice.
Email smtp port selection (Using 465?)
The ability to be able to AUTH using ‘telnet’ is extremely important in your first steps of email troubleshooting.
Port 465 (SMTP over SSL) is largely deprecated in favor of STARTTLS on 25. You may need to try alternate ports such as port 2525 or port 587 (Mail Submission) when things do not seem to work as expected.
Command Line SMTP tests for experienced sysadmins
If you’re comfortable with the command line, these might help diagnose network or certificate problems. If these do not seem “easy-to-follow” then you should please ignore this section.
See also Test SMTP Authentication and StartTLS.
Office 365 Tweaks
If you’re using Office 365, be sure to include these (the first line is what you are likely missing):
DISCOURSE_SMTP_AUTHENTICATION: login
DISCOURSE_SMTP_ENABLE_START_TLS: true
DISCOURSE_SMTP_PORT: 587
and set the correct notification_email (which is likely different from your forum hostname).
Email still doesn’t work! What next?
Anything else I forgot here? Feel free to edit this.
Debug issues with first connection to smtp server from inside the Discourse container
1. Enter your container:
./launcher enter app
2. Check dns resolving for your smtp server name via getent hosts:
(dig, nslookup, ping etc. are not installed inside the container.)
getent hosts your.smtp.server
Result on success:
# IPv4
123.123.123.123 your.smtp.server
# IPv6
2001:db8:0:0:0:ff00:42:8329 your.smtp.server
3. Try to open a connection to your smtp server via openssl:
(telnet, nc etc. are not installed inside the container.)
Fiddle with some different settings until you succeed with a connection.
openssl s_client -connect your.smtp.server:465
openssl s_client -connect your.smtp.server:587 -starttls smtp
# IPv4
openssl s_client -connect 172.17.0.123:465
openssl s_client -connect 172.17.0.123:587 -starttls smtp
# IPv6
openssl s_client -6 -connect "[2001:db8:0:0:0:ff00:42:8329]:465"
openssl s_client -6 -connect "[2001:db8:0:0:0:ff00:42:8329]:587" -starttls smtp
See: How to check SMTP connection → Step 3: Checking SMTP Connection Over TLS Using Openssl
4. Use your found working connection settings with Discourse.
Bonus: show Discourse IP from inside docker container
( ifconfig , ip etc. are not installed inside the container.)
hostname -I
Result like:
172.17.0.2