Fix: Clear stale relay mappings and remove config block when disabled

[hikmethankolay]

fixes #293

Purpose

When an SMTP relay is disabled or deleted, the system fails to fall back to the server's own/local SMTP and returns "mail transport unavailable" error. This occurs because:

1. Stale database entries: The bm_domain_smtp_transport table retains relay transport mappings pointing to non-existent SMTP services
2. Orphaned Postfix config: The main.cf relay configuration block (sender_dependent_default_transport_maps) remains active even after relay is disabled

This PR ensures proper cleanup when relay functionality is disabled, restoring expected fallback behavior.

Implementation

File: core/internal/service/relay/config_sync.go

Change 1 - Clear stale transport mappings (lines 443-447):

// Clear stale relay transport mappings to ensure fallback to original SMTP
_, err = g.DB().Model("bm_domain_smtp_transport").Where("atype", "relay").Delete()
if err != nil {
    g.Log().Warningf(ctx, "Failed to clear relay transport mappings: %v", err)
}

Change 2 - Remove relay config block from main.cf (lines 808-822):

} else {
    // Remove the configuration block when relay is disabled
    if hasConfigBlock {
        blockEnd := endIndex + len(endMarker)
        if blockEnd < len(content) && (content[blockEnd] == '\n' || content[blockEnd] == '\r') {
            blockEnd++
            if blockEnd < len(content) && content[blockEnd] == '\n' {
                blockEnd++
            }
        }
        content = content[:beginIndex] + content[blockEnd:]
        modified = true
        g.Log().Info(nil, "Removed relay configuration block from main.cf")
    }
}

Testing

• Unit tests passed (go test)
• Manual steps:

# 1. Configure and enable an SMTP relay with domain binding
# 2. Send test email → should route via relay
# 3. Disable the relay (set active=0)
# 4. Send test email → should now use local SMTP (fallback)
# 5. Verify main.cf no longer contains relay configuration block
docker exec billionmail-postfix-billionmail-1cat /etc/postfix/main.cf | grep -A4 "RELAY SERVICE"
# 6. Verify transport table is cleared
docker exec billionmail-pgsql-billionmail-1 psql -U billionmail  -d billionmail  -c "SELECT * FROM bm_domain_smtp_transport WHERE atype='relay';"

• Impact analysis: No changes to relay-enabled functionality; only affects cleanup on disable

[Copilot]

Pull request overview

This PR fixes issue #293 by ensuring proper cleanup when SMTP relay functionality is disabled or deleted. The changes prevent the "mail transport unavailable" error that previously occurred due to stale database entries and orphaned Postfix configuration.

Key changes:

• Clears relay transport mappings from the database when relay system becomes inactive
• Removes the relay configuration block from Postfix's main.cf when relay is disabled

---

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[Copilot]

Context parameter inconsistency: The logging call uses nil for the context parameter, but the pattern used elsewhere in this file when context is unavailable is context.Background() (see lines 705, 747, 756, 758). Using context.Background() instead of nil is more idiomatic and consistent with the rest of the codebase.

Suggested change

	g.Log().Info(nil, "Removed relay configuration block from main.cf")
	g.Log().Info(context.Background(), "Removed relay configuration block from main.cf")

[Copilot]

Newline handling could be more robust: The logic handles common cases like \n, \n\n, and \r\n, but doesn't consistently handle all newline character combinations. After checking for the first newline character (which could be \n or \r), the second check only looks for \n. Consider checking for any newline character in the second check as well to handle edge cases more consistently.

Suggested change

	if blockEnd < len(content) && content[blockEnd] == '\n' {
	if blockEnd < len(content) && (content[blockEnd] == '\n' || content[blockEnd] == '\r') {

[Copilot]

Error handling inconsistency: Similar database delete operation at line 863 returns an error when the delete fails, but here it only logs a warning. This inconsistency could mask database issues. Consider returning the error instead of just logging it to maintain consistent error handling behavior throughout the function.

Suggested change

	g.Log().Warningf(ctx, "Failed to clear relay transport mappings: %v", err)
	return gerror.Wrap(err, "Failed to clear relay transport mappings")