You can log in to your email account successfully, but outbound messages are not being delivered — recipients are not receiving them, or you are getting an error when sending.
Step 1: Test with Roundcube
Before checking client settings, open Roundcube (the webmail interface) and try sending a message. Roundcube uses the server's local mail stack directly, bypassing any client configuration issues. If Roundcube sends successfully but your email client does not, the problem is in your client's SMTP settings (go to Step 3). If Roundcube also fails, the problem is on the server side (go to Step 2).
Step 2: Server-Side Mail Log (Admin Task)
Outbound mail failures are logged on the server. This step requires admin access. Check the mail log:
tail -n 100 /var/log/mail.log
Look for lines containing your email address and look at the status= field. Common entries:
| Log entry | Meaning |
|---|---|
status=deferred (connect to ... Connection refused) |
Postfix can't reach the remote MX — usually port 25 blocked by your hosting provider |
status=bounced (host ... said: 550 ... SPF) |
Recipient's server rejected for SPF failure |
status=bounced (host ... said: 550 ... DKIM) |
Recipient's server rejected for DKIM failure |
status=sent |
Mail was delivered — the issue may be on the recipient side |
Step 3: Correct SMTP Settings
Use these settings in your email client (Thunderbird, Outlook, Apple Mail, etc.):
| Setting | Value |
|---|---|
| SMTP host | Your server's IP address or hostname |
| Port | 587 |
| Encryption | STARTTLS |
| Authentication | Normal password |
| Username | Your full email address (e.g. you@example.com) |
| Password | Your email account password |
[!IMPORTANT] Do not use port 25 in your email client. Port 25 is for server-to-server (MTA) delivery only. Client submission must use port 587.
Common Causes
Port 25 blocked by your hosting provider. Many VPS providers block outbound port 25 by default to prevent spam abuse. Postfix uses port 25 for server-to-server delivery, so if your provider blocks it, mail will be deferred indefinitely. The mail log will show Connection refused or Connection timed out when trying to reach remote MX servers.
To verify:
telnet gmail-smtp-in.l.google.com 25
If this hangs or is refused, port 25 is blocked. The solution is to configure an SMTP relay (a transactional mail provider like Mailgun, SendGrid, or Amazon SES) through Postfix. Contact your hosting admin to set this up.
SPF or DKIM not configured. Modern mail servers reject or spam-folder messages without valid SPF and DKIM records. If your domain's DNS was set up outside Opterius, these records may be missing. See SPF, DKIM, DMARC for the correct DNS records to add.
Wrong SMTP settings in email client. The most common user-side issue. Double-check the settings in the table above, particularly the port (587, not 465 or 25) and that the username is the full email address, not just the local part.