RoundCube Default ADMIN mailbox receives but can't send emails - Created mailboxes work fine

J

jeffbaygents

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Sep 25, 2025
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I created an unmanaged VPS using AlmaLinux 10, OpenLiteSpeed, & DirectAdmin, using a domain of "srvsystem.com". For years, I use my long checklist to ensure consistency each time I create a new VPS, and I update it for any changes each time. I try to stay with default settings along the way for everything, which reduces problems for getting a solid, reliable base install.

With that said, I'm near the end of the checklist and was testing sending and receiving emails from the default "admin" mailbox. I discovered it can readily receive emails but it can't send emails. These are the things I've done:

  • I had already requested some SMTP ports to be opened from my host provider, as I've done before in the past.
  • In RoundCube (Settings | Identities), using its default admin mailbox, I changed its default "...local" email address to a regular "...srvsystem.com" email address.
  • I tested receiving emails from a Gmail account; it worked fine. I tested sending to the same Gmail account and it fails with "SMTP error 535... Authentication failed".
  • I created a new mailbox and tested its sending & receiving. Works fine.

I've already seen a similar issue mentioned elsewhere this year (2025). It was mentioned to fix it by running a CLI of
$config[‘smtp_server’] = ‘tls://%t’;

Why I don't run that "Fix/Workaround" & am looking for a confirmed solution:
  • I haven't run that script because I don't know what it does & I don't know how to reverse it, if there are issues.
  • I don't know how to read my current config with what the current setting is.
  • Also, I haven't run it because all mailboxes but this default one work fine.
  • Also, no one using this "workaround/fix" mentions that this issue only fails with the default mailbox and other mailboxes are fine (they might not be aware of this).
  • I'm concerned about the impact as, maybe this aspect of the default admin mailbox not sending out emails is by design for security reasons.
  • DirectAdmin (sometimes) prefers various settings to be set using inside DirectAdmin and not via CLI. Also, this might just be a RoundCube thing, and nothing to do with DirectAdmin.

I'm stuck and halted further setup of this VPS so, any guidance on this is greatly appreciated. Also, I rebuilt this VPS a second time and am assured it's a repeated issue. Thanks.
 
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Just a question, who are you hosting the VPS with? Some providers block ports 25 and 465 by default. Digitalocean (I believe) you've no chance in getting them unblocked. Hetzner you can get the ports opened with a request, Contabo I believe are open as well. It's a security feature most responsible hosts put in place while they do the "Know your customer" bits to make sure you won't abuse the server.

Try:
Bash: 
# nc -vz smtp.gmail.com 25
# nc -vz smtp.gmail.com 465

This is what you'll see if your outgoing port is open:

1759008928904.png


Failing that, for now, can you relay mail via port 587 to a reliable smtp host until you resolve the issue?
 
Thanks but, you might have missed the part where all mailboxes work fine, except the default one.
 
jeffbaygents said:
Thanks but, you might have missed the part where all mailboxes work fine, except the default one.
Click to expand...
Apologies, you're right I did miss that. 535 is an authentication error where the username/password might be wrong. I've never used the actual admin email account on the server, only ever created email accounts. would changing the password of the admin email account help? see if that works? I'm not sure if it defaults to your admin password in /usr/local/directadmin/conf/setup.txt .

And to help you out with the $config['smtp_server'] in roundcube, here's some of my my settings that work. I've just sent a successful test message to another email address from the server admin email. The tls part of the bit you're querying is just the protocol to connect to the remote server on over the port. As yuou're worring about making changes and rolling back mistakes, If you ever make any changes to a config file, my advice is to copy the file first ( # cp file.conf file.conf.bak ) so you can roll back at any time. Hope this may help?

Bash: 
root@s3 /var/www/html/roundcube/config # cat config.inc.php
<?php

$config = [];

$config['imap_host'] = 'localhost:143';
$config['smtp_host'] = 'localhost:587';

$config['login_autocomplete'] = 2;
$config['quota_zero_as_unlimited'] = true;
$config['email_dns_check'] = true;

// List of active plugins (in plugins/ directory)
//
// The 'managesieve' plugin will be configured and enabled here automatically
// by CustomBuild if Dovecot pigeonhole is enabled.
$config['plugins'] = ['managesieve','password','archive','zipdownload'];

// skin name: folder from skins/
$config['skin'] = 'elastic';
 
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Thanks DrWizzle for your help. My config matched yours too. However, I have fixed it and found out why. On my other VPS server, it uses Apache and AlmaLinux 9.6 with several extra installs. But on this VPS server I'm not using Apache and I'm using OpenLiteSpeed with AlmaLinux 10.x. Because of that I left out several of the things I would normally install because of Apache but I wasn't sure what would be usable since it was an OpenLitespeed server. With that said, I had left out EPEL. So, apparently something in EPEL gave it extra functionality for the admin mailbox.

So, for others who might need this, here's what resolved it for me. However, it was a fix that was used during the building of the server. I'm unsure if it would fix it for others for a pre-existing server. Here are the CLI scripts I ran:

  • dnf update -y
  • dnf install -y wget epel-release
  • sudo dnf check-update && sudo dnf update
  • reboot
 
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