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Sorry to hear you’re facing problems 
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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 20.0.5): 25.0.1
Operating system and version (eg, Ubuntu 20.04): Ubuntu 22.04
Apache or nginx version (eg, Apache 2.4.25): Apache2
PHP version (eg, 7.4): 8.1
The issue you are facing:
I set up Nextcloud and it’s working fine except for when I try to set up my email account (hosted on gandi.net) in the Mail app. When I try to use manual setup, I keep getting the message “SMTP connection failed”. When I try an app on my PC like Thunderbird it works flawlessly.
I’ve seen similar topics and people have had some succes with different port settings but I’ve tried different combinations like None/SSL/STARTTLS and all the SMTP ports on the Gandi page but none of that works. I’ve not made any changes to any config files with email in mind.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- Enter the SMTP information as described on How to Set Up Your Email Client to Work with Email Hosted by Gandi | Email - Standard Email Settings | Gandi Documentation — Gandi Documentation documentation
The output of your Nextcloud log in Admin > Logging:
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The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
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The output of your Apache/nginx/system log in /var/log/____:
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PASTE HERE
Output errors in nextcloud.log in /var/www/ or as admin user in top right menu, filtering for errors. Use a pastebin service if necessary.
I don't think this is necessary but do tell me if it helps.