diff --git a/imapserver/server.go b/imapserver/server.go
index 5c4971f..b984208 100644
--- a/imapserver/server.go
+++ b/imapserver/server.go
@@ -1435,7 +1435,8 @@ func (c *conn) cmdStarttls(tag, cmd string, p *parser) {
 		xcheckf(err, "reading buffered data for tls handshake")
 		conn = &prefixConn{buf, conn}
 	}
-	c.ok(tag, cmd)
+	// We add the cid to facilitate debugging in case of TLS connection failure.
+	c.ok(tag, cmd+" ("+mox.ReceivedID(c.cid)+")")
 
 	cidctx := context.WithValue(mox.Context, mlog.CidKey, c.cid)
 	ctx, cancel := context.WithTimeout(cidctx, time.Minute)
diff --git a/smtpserver/server.go b/smtpserver/server.go
index 691b0b3..b63e964 100644
--- a/smtpserver/server.go
+++ b/smtpserver/server.go
@@ -880,7 +880,8 @@ func (c *conn) cmdStarttls(p *parser) {
 		}
 	}
 
-	c.writecodeline(smtp.C220ServiceReady, smtp.SeOther00, "go!", nil)
+	// We add the cid to the output, to help debugging in case of a failing TLS connection.
+	c.writecodeline(smtp.C220ServiceReady, smtp.SeOther00, "go! ("+mox.ReceivedID(c.cid)+")", nil)
 	tlsConn := tls.Server(conn, c.tlsConfig)
 	cidctx := context.WithValue(mox.Context, mlog.CidKey, c.cid)
 	ctx, cancel := context.WithTimeout(cidctx, time.Minute)