Resolved Issue Sending Emails via Plesk Using Mailbox.org SMTP

[sauerleander]

Server operating system version

Ubuntu 24.04

Plesk version and microupdate number

18.0.56 #2

Hello Plesk Community,





I am experiencing an issue where I cannot send emails from my Plesk instance. The instance is configured to use Mailbox.org as the SMTP server on port 465. The credentials work correctly outside of Plesk, so I suspect the problem is related to the Plesk setup itself.





Here are some technical details (sensitive information removed for public posting):

• Web Server: [Web Server Name]
• License: [IONOS SE License – not publicly shared]
• Hosting via IONOS SE

Has anyone encountered a similar issue or can suggest what might be causing this? I can provide additional sensitive details privately if needed for troubleshooting.





Thanks in advance for any guidance or suggestions!





Best regards

 

[Sebahat.hadzhi]

Hi, @sauerleander . The first thing that comes to mind is port 465 being blocked. Have you confirmed it is open on the server and on IONOS' end? Are there any more details you can provide on the experienced issue - errors, logs or bounce back messages?

 

[sauerleander]

Hi @Sebahat.hadzhi,



thank you for your suggestions. I believe the issue is finally resolved. The root cause was that I recently regained multiple domains from my hosting provider and forgot to update the server hostname accordingly.



As a small improvement suggestion, it would be great if Plesk allowed configuring which sender address should be used directly when setting up external SMTP servers. I haven’t been able to find this option yet.



Additionally, I have a few questions:

1. Is HTTP/3 officially supported? I’ve heard from another host that also provides licenses through you that it might still be in some kind of beta.
2. As a customer whose license is obtained via IONOS SE, am I theoretically able to open support tickets directly with Plesk for issues like these?
3. Does the system automatically handle all updates for both Plesk and Ubuntu, including major Ubuntu updates? And what happens with packages that have been installed manually — are they affected or left untouched?

Thanks in advance for your guidance!

 

[scsa20]

Is HTTP/3 officially supported? I’ve heard from another host that also provides licenses through you that it might still be in some kind of beta.

It's an experimental feature of nginx (and thus plesk). The specification is still new being released this year. You can still enabled it (like I did). You can learn more about it over at (Plesk for Linux) HTTP/3 Support in Plesk

As a customer whose license is obtained via IONOS SE, am I theoretically able to open support tickets directly with Plesk for issues like these?

Yes, refer to https://support.plesk.com/hc/en-us/articles/12388090147095-How-to-get-support-directly-from-Plesk

Does the system automatically handle all updates for both Plesk and Ubuntu, including major Ubuntu updates? And what happens with packages that have been installed manually — are they affected or left untouched?

Plesk can handle all system updates depending on how you configured the settings in Tools & Settings > System Updates. See (Plesk for Linux) System Updates for more information.

 

[sauerleander]

Hello @sca20,





Thank you for the information regarding HTTP/3 and the update mechanisms. I have already enabled HTTP/3 and wanted to ask if there is anything specific I should be aware of, or if Plesk essentially handles all maintenance for me.





My current settings are as follows:





General

• Automatically install Plesk updates (recommended)
• Automatically install updates for third-party components provided by Plesk
• Automatically install system package updates
  (This also includes updates for third-party components provided by Plesk.)

Access Plesk Installer via Hostname and Port

• Access the Plesk Installer web interface without opening TCP port 8447 additionally in the firewall.

Secure Updates

• Updates for system packages are installed from the repository where the packages were originally installed.
• Secure updates for system packages are enabled.
  (Recommended to use only secure updates if you are not an advanced user, to avoid negative impact on server functionality.)

Notifications

• Notify about available and installed system package updates

Could you please confirm if these settings are sufficient for Plesk to essentially handle all maintenance, or if there are any additional points I should pay attention to?





Thank you in advance for your feedback.





Best regards

 

[Kaspar]

Thank you for the information regarding HTTP/3 and the update mechanisms. I have already enabled HTTP/3 and wanted to ask if there is anything specific I should be aware of, or if Plesk essentially handles all maintenance for me.

As for HTTP/3 the known limitations are listed on the Plesk documentation page. If anything changes regarding HTTP/3 with nginx (and as a result with Plesk), these changes will likely be published in the change log. Note that as HTTP/3 is considered experimental, any changes are not likely to be announced well in advance. Since you've enabled automatic updates, any Plesk updates (including anything related to HTTP/3) will be installed automatically.

In more generic terms regarding maintenance and updates; Plesk is a server administrator tool. Helping you (as a system administrator) manage a server for hosting purposes. It's not an OS, nor does it completely automate all of the sys admin responsibilities. It's still the sys admins job to secure and maintain the server. For example, Plesk does not update the kernel and (generally) also does not automatically upgrade the OS or any applications to new major versions to prevent things from breaking. Which means that if you want to upgrade to a new major release of your OS, say from Ubuntu 24.04 to 26.04, you'll have to manually prepare and initiate the upgrade. Same goes for applications, if you want to upgrade to the newest supported MariaDB release, you'll have to initiate that yourself. (For MariaDB there is a Plesk tool to help you with that).

Small side note, please keep an eye on your post formatting, using that many empty lines in your posts does not improve readability for others on the forum trying to help in answering your questions.