diff --git a/autotests/kemailaddresstest.cpp b/autotests/kemailaddresstest.cpp
--- a/autotests/kemailaddresstest.cpp
+++ b/autotests/kemailaddresstest.cpp
@@ -342,7 +342,6 @@
 {
     QFETCH(QString, input);
     QFETCH(bool, expResult);
-
     QCOMPARE(isValidSimpleAddress(input), expResult);
 }
 
diff --git a/src/kemailaddress.cpp b/src/kemailaddress.cpp
--- a/src/kemailaddress.cpp
+++ b/src/kemailaddress.cpp
@@ -21,10 +21,9 @@
 #include "kcodecs.h"
 #include "kcodecs_debug.h"
 
-#include <QUrl>
-
-#include <QRegExp>
 #include <QByteArray>
+#include <QRegularExpression>
+#include <QUrl>
 
 using namespace KEmailAddress;
 
@@ -627,20 +626,24 @@
         }
     }
 
-    QString addrRx;
+    // Anchor the pattern with \A (here) and \z (at the end)
+    // to match the whole subject string
+    QString addrRx(QStringLiteral("\\A"));
 
     if (localPart[ 0 ] == QLatin1Char('\"') || localPart[ localPart.length() - 1 ] == QLatin1Char('\"')) {
-        addrRx = QStringLiteral("\"[a-zA-Z@]*[\\w.@-]*[a-zA-Z0-9@]\"@");
+        addrRx += QStringLiteral("\"[a-zA-Z@]*[\\w.@-]*[a-zA-Z0-9@]\"@");
     } else {
-        addrRx = QStringLiteral("[a-zA-Z]*[~|{}`\\^?=/+*'&%$#!_\\w.-]*[~|{}`\\^?=/+*'&%$#!_a-zA-Z0-9-]@");
+        addrRx += QStringLiteral("[a-zA-Z]*[~|{}`\\^?=/+*'&%$#!_\\w.-]*[~|{}`\\^?=/+*'&%$#!_a-zA-Z0-9-]@");
     }
     if (domainPart[ 0 ] == QLatin1Char('[') || domainPart[ domainPart.length() - 1 ] == QLatin1Char(']')) {
-        addrRx += QStringLiteral("\\[[0-9]{,3}(\\.[0-9]{,3}){3}\\]");
+        addrRx += QStringLiteral("\\[([0-9]{1,3}\\.){1,3}([0-9]{1,3})\\]");
     } else {
-        addrRx += QStringLiteral("[\\w-#]+(\\.[\\w-#]+)*");
+        addrRx += QStringLiteral("[\\w#-]+(\\.[\\w#-]+)*");
     }
-    QRegExp rx(addrRx);
-    return  rx.exactMatch(aStr) && !tooManyAtsFlag;
+    addrRx += QStringLiteral("\\z");
+
+    QRegularExpression rx(addrRx, QRegularExpression::UseUnicodePropertiesOption);
+    return  rx.match(aStr).hasMatch() && !tooManyAtsFlag;
 }
 
 //-----------------------------------------------------------------------------
@@ -1113,7 +1116,7 @@
 {
     QString quoted = str;
 
-    QRegExp needQuotes(QStringLiteral("[^ 0-9A-Za-z\\x0080-\\xFFFF]"));
+    QRegularExpression needQuotes(QStringLiteral("[^ 0-9A-Za-z\\x0080-\\xFFFF]"));
     // avoid double quoting
     if ((quoted[0] == QLatin1Char('"')) && (quoted[quoted.length() - 1] == QLatin1Char('"'))) {
         quoted = QLatin1String("\"") + escapeQuotes(quoted.mid(1, quoted.length() - 2)) + QLatin1String("\"");