I opened a ticket for this same problem a couple of days ago but I cannot find it on the forum anymore.
I performed a package updates from Webmin interface and since then I’m having the following problems:
The Usermin interface stop working “https://:20000” and I have to restart the server so it work back again.
When trying to send an email with Usermin I got the following error: “Failed to send mail : SMTP command failed”.
Email procesing with the Outlook client works just find (sending and receiving).
I’m not an expert on this platform so I don’t know when to start looking.
I’ve read many posts on the same subject on the forum, but not of them provides me with any clue on how to fix this.
Here is the platform information for your reference:
CentOS Linux 8.4.2105
Webmin version 1.973
Usermin version 1.823
Virtualmin version 6.16 Pro
Authentic theme version 19.73