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---
title: 'Troubleshooting | Debugging'
---
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!!! info "Contributions Welcome!"
Please contribute your solutions to help the community :heart:
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## Enable Verbose Debugging Output
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You may find it useful to enable the [`DMS_DEBUG`][github-file-env-dmsdebug] environment variable.
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## Invalid Username or Password
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1. Shell into the container:
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```sh
docker exec -it < my-container > bash
```
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2. Check log files in `/var/log/mail` could not find any mention of incorrect logins here neither in the dovecot logs.
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3. Check the supervisors logs in `/var/log/supervisor` . You can find the logs for startup of fetchmail, postfix and others here - they might indicate problems during startup.
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4. Make sure you set your hostname to `mail` or whatever you specified in your `docker-compose.yml` file or else your FQDN will be wrong.
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## Installation Errors
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During setup, if you get errors trying to edit files inside of the container, you likely need to install `vi` :
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```sh
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sudo su
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docker exec -it < my-container > apt-get install -y vim
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```
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## Testing Connection
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I spent HOURS trying to debug "Connection Refused" and "Connection closed by foreign host" errors when trying to use telnet to troubleshoot my connection. I was also trying to connect from my email client (macOS mail) around the same time. Telnet had also worked earlier, so I was extremely confused as to why it suddenly stopped working. I stumbled upon `fail2ban.log` in my container. In short, when trying to get my macOS client working, I exceeded the number of failed login attempts and fail2ban put dovecot and postfix in jail! I got around it by whitelisting my ipaddresses (my ec2 instance and my local computer)
```sh
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sudo su
docker exec -ti mail bash
cd /var/log
cat fail2ban.log | grep dovecot
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# Whitelist IP addresses:
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fail2ban-client set dovecot addignoreip < server ip > # Server
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fail2ban-client set postfix addignoreip < server ip >
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fail2ban-client set dovecot addignoreip < client ip > # Client
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fail2ban-client set postfix addignoreip < client ip >
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# This will delete the jails entirely - nuclear option
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fail2ban-client stop dovecot
fail2ban-client stop postfix
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```
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## Sent email is never received
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Some hosting provides have a stealth block on port 25. Make sure to check with your hosting provider that traffic on port 25 is allowed
Common hosting providers known to have this issue:
- [Azure ](https://docs.microsoft.com/en-us/azure/virtual-network/troubleshoot-outbound-smtp-connectivity )
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- [AWS EC2 ](https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/ )
[github-file-env-dmsdebug]: https://github.com/docker-mailserver/docker-mailserver/blob/master/ENVIRONMENT.md#dms_debug