diff -r aafdfb27dde1 -r 6c34689e894a data/dictionary.xml
--- a/data/dictionary.xml	Mon Aug 12 15:05:25 2013 +0200
+++ b/data/dictionary.xml	Mon Aug 12 18:12:50 2013 +0200
@@ -196,7 +196,17 @@
 	</concept>
 	<concept>
 		<term abbreviation="MUA" completeForm="mail user agent" language="en"/>
-		<explanation language="en"><text>an e-mail client software</text></explanation>
+		<explanation language="en">
+			<text>
+				an e-mail client – a software used for managing user's e-mail;
+				because the MUA (like most client software) runs only when user needs it,
+					the messages from the Internet are received by a remote MTA over the SMTP protocol,
+					then delivered using an MDA into user's remote mailbox,
+					from which they are obtained by the MUA using POP3 or IMAP4 protocols;
+				when sending an e-mail, the MUA composes the message in RFC 5322 format and then submits it using the SMTP protocol to a MTA or MSA server;
+				examples of MUA: Mozilla Thunderbird, KMail, Evolution, Mutt, Lotus Notes
+			</text>
+		</explanation>
 		<tag>computer</tag>
 		<tag>messaging</tag>
 	</concept>
@@ -207,6 +217,12 @@
 		<tag>messaging</tag>
 	</concept>
 	<concept>
+		<term abbreviation="MSA" completeForm="message submission agent " language="en"/>
+		<explanation language="en"><text></text></explanation>
+		<tag>computer</tag>
+		<tag>messaging</tag>
+	</concept>
+	<concept>
 		<term abbreviation="MDA" completeForm="message delivery agent " language="en"/>
 		<explanation language="en"><text></text></explanation>
 		<tag>computer</tag>