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Guide BillionMail Webmail (Roundcube) Not Working: Login, Connection and Sending Errors - Printable Version

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BillionMail Webmail (Roundcube) Not Working: Login, Connection and Sending Errors - JAY - 10-23-2026

BillionMail webmail (Roundcube) not working: login, connection and sending errors

BillionMail includes Roundcube, a webmail where you read and answer mail for your mailboxes (support@, hello@ and so on). This guide covers the problems people hit most: the page won't open, login fails, mail won't send, or new mail never shows up.

Where is webmail?
Code:
https://your-mail-host/roundcube/
If your BillionMail uses a custom HTTPS port, include it:
Code:
https://your-mail-host:PORT/roundcube/
.

Problem 1: "Login failed"
  • Use the full email address as the username, e.g.
    Code:
    [email protected]
    , not just "support".
  • Use the mailbox password, not your BillionMail admin password. They're different.
  • Not sure of the password? In BillionMail, open Mailboxes, edit the mailbox and set a new one.
  • Still failing? The login check is done by the Dovecot container. See Problem 2.

Problem 2: "Connection to storage server failed"
Roundcube can't reach Dovecot, the part that stores mail. Open Settings > Service in BillionMail and check that every service (postfix, dovecot, webmail, rspamd, pgsql, redis) says Running. Click Restart next to dovecot and then webmail.
[Image: attachment.php?aid=426]

From the command line, first list your container names:
Code:
docker ps --format "{{.Names}}" | grep -i billionmail
You'll see names like
Code:
billionmail_xxxx-dovecot-billionmail-1
. Use yours in place of DOVECOT and WEBMAIL:
Code:
docker restart DOVECOT WEBMAIL docker logs --tail 50 DOVECOT
Errors about certificates or "Permission denied" in that log point to the real cause.

Problem 3: "SMTP Error (535): Authentication failed" when sending
Reading works, sending doesn't. Roundcube hands outgoing mail to Postfix, which checks the password with Dovecot.
  • Log out of webmail and in again (an old session can keep an old password).
  • Restart postfix and dovecot in Settings > Service.
  • Check the mail log from your BillionMail folder (
    Code:
    /www/dk_project/dk_app/billionmail/billionmail_XXXX
    on aaPanel):
    Code:
    tail -n 50 logs/postfix/mail.log

Problem 4: Blank page, 502 or 504 error
The webmail container (Roundcube runs on PHP-FPM) isn't answering. Restart webmail in Settings > Service, wait 20 seconds and reload. If it comes back, check its log:
Code:
docker logs --tail 50 WEBMAIL
A full disk also causes this. Check with
Code:
df -h
.

Problem 5: You can log in, but new mail never arrives
Sending and receiving are separate. For receiving, the internet must find and reach your server:
  • MX record:
    Code:
    dig +short MX news.example.com
    must show your mail host.
  • Incoming port 25: from another computer,
    Code:
    nc -vz -w 5 your-mail-host 25
    must connect. Open port 25 in aaPanel's Security page and your provider's firewall.
  • Cloudflare: the mail host record must be DNS only (grey cloud).
Send a test from a Gmail account. If Gmail returns a bounce message, it tells you exactly why.

Using a mail app instead (Outlook, Thunderbird, phone)
The Copy link under "Login info" on the Mailboxes page gives you the settings. Usually:
  • Incoming (IMAP): your mail host, port 993, SSL/TLS
  • Outgoing (SMTP): your mail host, port 465 (SSL/TLS) or 587 (STARTTLS), login required
  • Username: the full email address
Open ports 993, 465 and 587 in aaPanel's Security page. A certificate warning in the app means you haven't applied a Let's Encrypt certificate yet; see BillionMail SSL and hostname fix.

Sources: BillionMail on GitHub ยท Roundcube wiki


More BillionMail troubleshooting
Applies to BillionMail 4.9 installed through aaPanel or the install script, October 2026.