diff --git a/.gitignore b/.gitignore
index 91a5ca7..9818eb8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,5 @@
 .project
 .classpath
 .checkstyle
+/.idea
+/*.iml
diff --git a/src/main/java/net/markenwerk/utils/mail/smime/SmimeUtil.java b/src/main/java/net/markenwerk/utils/mail/smime/SmimeUtil.java
index 60b6e46..e900e49 100644
--- a/src/main/java/net/markenwerk/utils/mail/smime/SmimeUtil.java
+++ b/src/main/java/net/markenwerk/utils/mail/smime/SmimeUtil.java
@@ -53,6 +53,7 @@
 import javax.mail.internet.MimeMultipart;
 import javax.mail.internet.MimePart;
 
+import com.sun.mail.smtp.SMTPMessage;
 import org.bouncycastle.asn1.ASN1EncodableVector;
 import org.bouncycastle.asn1.cms.AttributeTable;
 import org.bouncycastle.asn1.cms.IssuerAndSerialNumber;
@@ -60,7 +61,10 @@
 import org.bouncycastle.asn1.smime.SMIMECapability;
 import org.bouncycastle.asn1.smime.SMIMECapabilityVector;
 import org.bouncycastle.asn1.smime.SMIMEEncryptionKeyPreferenceAttribute;
+import org.bouncycastle.asn1.x500.RDN;
 import org.bouncycastle.asn1.x500.X500Name;
+import org.bouncycastle.asn1.x500.style.BCStyle;
+import org.bouncycastle.asn1.x500.style.IETFUtils;
 import org.bouncycastle.cert.X509CertificateHolder;
 import org.bouncycastle.cert.jcajce.JcaCertStore;
 import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
@@ -390,23 +394,28 @@ private static JcaCertStore getCertificateStore(SmimeKey smimeKey) throws Certif
 		}
 		return new JcaCertStore(certificateList);
 	}
-
+	
 	/**
 	 * Signs a MIME message and yields a new S/MIME signed MIME message.
-	 * 
+	 *
 	 * @param session
 	 *            The {@link Session} that is used in conjunction with the
 	 *            original {@link MimeMessage}.
 	 * @param mimeMessage
-	 *            The original {@link MimeMessage} to be signed.
+	 *            The original {@link MimeMessage} or {@link SMTPMessage} to be signed.
 	 * @param smimeKey
 	 *            The {@link SmimeKey} used to obtain the {@link PrivateKey} to
 	 *            sign the original message with.
-	 * @return The new S/MIME signed {@link MimeMessage}.
+	 * @return The new S/MIME signed {@link MimeMessage} or {@link SMTPMessage}.
 	 */
-	public static MimeMessage sign(Session session, MimeMessage mimeMessage, SmimeKey smimeKey) {
+	public static <T extends MimeMessage> T sign(Session session, T mimeMessage, SmimeKey smimeKey) {
+		return (mimeMessage instanceof SMTPMessage)
+				? sign(mimeMessage, (T) new SMTPMessage(session), smimeKey)
+				: sign(mimeMessage, (T) new MimeMessage(session), smimeKey);
+	}
+	
+	private static <T extends MimeMessage> T sign(T mimeMessage, T signedMessage, SmimeKey smimeKey) {
 		try {
-			MimeMessage signedMessage = new MimeMessage(session);
 			copyHeaderLines(mimeMessage, signedMessage);
 			copyContent(sign(extractMimeBodyPart(mimeMessage), smimeKey), signedMessage);
 			return signedMessage;
@@ -491,6 +500,61 @@ private static boolean checkSignature(SMIMESigned smimeSigned) throws MessagingE
 			throw handledException(e);
 		}
 	}
+	
+	/**
+	 * @param mimeMultipart
+	 *            The {@link MimeMultipart} to be checked.
+	 * @return The subject / address to which the certificate was issued to. Email clients may use this to show
+	 * 			{@code "Signed by: <subject / address>"}
+	 */
+	public static String getSignedByAddress(MimeMultipart mimeMultipart) {
+		try {
+			return getSignedByAddress(new SMIMESigned(mimeMultipart));
+		} catch (Exception e) {
+			throw handledException(e);
+		}
+	}
+	
+	/**
+	 * @param mimePart
+	 *            The {@link MimePart} to be checked.
+	 * @return The subject / address to which the certificate was issued to. Email clients may use this to show
+	 * 			{@code "Signed by: <subject / address>"}
+	 */
+	public static String getSignedByAddress(MimePart mimePart) {
+		try {
+			if (mimePart.isMimeType("multipart/signed")) {
+				return getSignedByAddress(new SMIMESigned((MimeMultipart) mimePart.getContent()));
+			} else if (mimePart.isMimeType("application/pkcs7-mime") || mimePart.isMimeType("application/x-pkcs7-mime")) {
+				return getSignedByAddress(new SMIMESigned(mimePart));
+			} else {
+				throw new SmimeException("Message not signed");
+			}
+		} catch (Exception e) {
+			throw handledException(e);
+		}
+	}
+	
+	/**
+	 * Returns the subject / address to which the certificate was issued to. Email clients may use this to show
+	 * {@code "Signed by: <subject / address>"}
+	 */
+	private static String getSignedByAddress(SMIMESigned smimeSigned) {
+		try {
+			@SuppressWarnings("rawtypes")
+			Store certificates = smimeSigned.getCertificates();
+			
+			SignerInformation signerInformation = smimeSigned.getSignerInfos().getSigners().iterator().next();
+			X509Certificate certificate = getCertificate(certificates, signerInformation.getSID());
+			SignerInformationVerifier verifier = getVerifier(certificate);
+			X500Name x500name = verifier.getAssociatedCertificate().getSubject();
+			RDN cn = x500name.getRDNs(BCStyle.CN)[0];
+			return IETFUtils.valueToString(cn.getFirst().getValue());
+			
+		} catch (Exception e) {
+			throw handledException(e);
+		}
+	}
 
 	private static X509Certificate getCertificate(@SuppressWarnings("rawtypes") Store certificates, SignerId signerId)
 			throws CertificateException {