diff --git a/src/imapfilter.c b/src/imapfilter.c
index 6206e78..78d4c37 100644
--- a/src/imapfilter.c
+++ b/src/imapfilter.c
@@ -21,7 +21,7 @@
 #endif
 
 
-extern buffer ibuf, obuf, nbuf;
+extern buffer ibuf, obuf, nbuf, cbuf;
 extern regexp responses[];
 
 options opts;			/* Program options. */
@@ -98,6 +98,7 @@ main(int argc, char *argv[])
 	buffer_init(&ibuf, INPUT_BUF);
 	buffer_init(&obuf, OUTPUT_BUF);
 	buffer_init(&nbuf, NAMESPACE_BUF);
+	buffer_init(&cbuf, CONVERSION_BUF);
 
 	if (opts.config == NULL)
 		opts.config = get_filepath("config.lua");
@@ -137,6 +138,7 @@ main(int argc, char *argv[])
 	buffer_free(&ibuf);
 	buffer_free(&obuf);
 	buffer_free(&nbuf);
+	buffer_free(&cbuf);
 
 	xfree(env.home);
 
diff --git a/src/imapfilter.h b/src/imapfilter.h
index 5fb85ee..d08b513 100644
--- a/src/imapfilter.h
+++ b/src/imapfilter.h
@@ -53,7 +53,8 @@
 /* Initial buffer size for input, output and namespace buffers. */
 #define INPUT_BUF			4096
 #define OUTPUT_BUF			1024
-#define NAMESPACE_BUF			128
+#define NAMESPACE_BUF			512
+#define CONVERSION_BUF			512
 
 /* Maximum length, in bytes, of a utility's input line. */
 #ifndef LINE_MAX
diff --git a/src/namespace.c b/src/namespace.c
index 6f0e0b5..779a5a4 100644
--- a/src/namespace.c
+++ b/src/namespace.c
@@ -1,11 +1,18 @@
 #include <stdio.h>
 #include <string.h>
+#include <iconv.h>
+#include <errno.h>
 
 #include "imapfilter.h"
 #include "buffer.h"
 
 
 buffer nbuf;			/* Namespace buffer. */
+buffer cbuf;			/* Conversion buffer. */
+
+
+const char *apply_conversion(const char *mbox);
+const char *reverse_conversion(const char *mbox);
 
 
 /*
@@ -17,26 +24,29 @@ apply_namespace(const char *mbox, char *prefix, char delim)
 {
 	int n;
 	char *c;
+	const char *m;
+
+	if (!strcasecmp(mbox, "INBOX"))
+		return mbox;
+
+	m = apply_conversion(mbox);
 
 	if ((prefix == NULL && delim == '\0') ||
-	    (prefix == NULL && delim == '/') ||
-	    !strcasecmp(mbox, "INBOX"))
-		return mbox;
+	    (prefix == NULL && delim == '/'))
+		return m;
 
 	buffer_reset(&nbuf);
 
 	n = snprintf(nbuf.data, nbuf.size + 1, "%s%s", (prefix ? prefix : ""),
-	    mbox);
+	    m);
 	if (n > (int)nbuf.size) {
 		buffer_check(&nbuf, n);
-		snprintf(nbuf.data, nbuf.size + 1, "%s%s",
-		    (prefix ? prefix : ""), mbox);
+		snprintf(nbuf.data, nbuf.size + 0, "%s%s",
+		    (prefix ? prefix : ""), m);
 	}
-	c = nbuf.data;
-	while ((c = strchr(c, '/')))
-		*(c++) = delim;
+	for (c = nbuf.data; (c = strchr(c, '/')) != NULL; *(c++) = delim);
 
-	debug("namespace: '%s' -> '%s'\n", mbox, nbuf.data);
+	debug("namespace: '%s' -> '%s'\n", m, nbuf.data);
 
 	return nbuf.data;
 }
@@ -52,11 +62,13 @@ reverse_namespace(const char *mbox, char *prefix, char delim)
 	int n, o;
 	char *c;
 
-	if ((prefix == NULL && delim == '\0') ||
-	    (prefix == NULL && delim == '/') ||
-	    !strcasecmp(mbox, "INBOX"))
+	if (!strcasecmp(mbox, "INBOX")) 
 		return mbox;
 
+	if ((prefix == NULL && delim == '\0') ||
+	    (prefix == NULL && delim == '/'))
+		return reverse_conversion(mbox);
+
 	buffer_reset(&nbuf);
 
 	o = strlen(prefix ? prefix : "");
@@ -68,11 +80,161 @@ reverse_namespace(const char *mbox, char *prefix, char delim)
 		buffer_check(&nbuf, n);
 		snprintf(nbuf.data, nbuf.size + 1, "%s", mbox + o);
 	}
-	c = nbuf.data;
-	while ((c = strchr(c, delim)))
-		*(c++) = '/';
+	for (c = nbuf.data; (c = strchr(c, delim)) != NULL; *(c++) = '/');
 
 	debug("namespace: '%s' <- '%s'\n", mbox, nbuf.data);
 
+	return reverse_conversion(nbuf.data);
+}
+
+
+/*
+ * Convert a mailbox name to the modified UTF-7 encoding, according to RFC 3501
+ * Section 5.1.3.
+ */
+const char *
+apply_conversion(const char *mbox)
+{
+	size_t n;
+	iconv_t cd;
+	char *inbuf, *outbuf;
+	size_t inlen, outlen;
+	char *c, *shift;
+
+	n = strlen(mbox);
+	buffer_check(&nbuf, n); 
+	buffer_reset(&nbuf);
+	xstrncpy(nbuf.data, mbox, *(mbox + n - 1) == '*' ||
+	    *(mbox + n - 1) == '%' ? n - 1 : n);
+	for (c = nbuf.data; (c = strchr(c, '&')) != NULL; *c = '+');
+
+	do {
+		inbuf = nbuf.data;
+		inlen = strlen(nbuf.data);
+
+		buffer_check(&cbuf, inlen);
+		buffer_reset(&cbuf);
+
+		outbuf = cbuf.data;
+		outlen = cbuf.size;
+
+		cd = iconv_open("UTF-7", "");
+		if (cd == (iconv_t)-1) {
+			error("converting mailbox name; %s\n", strerror(errno));
+			return mbox;
+		}
+		while (inlen > 0) {
+			if (iconv(cd, &inbuf, &inlen, &outbuf, &outlen) == -1) {
+				if (errno == E2BIG) {
+					buffer_check(&cbuf, cbuf.size * 2);
+					break;
+				} else {
+					error("converting mailbox name; %s\n",
+					    strerror(errno));
+					return mbox;
+				}
+			} else {
+				iconv(cd, NULL, NULL, &outbuf, &outlen);
+			}
+		}
+		iconv_close(cd);
+	} while (inlen > 0);
+
+	if (*outbuf != '\0')
+		*outbuf = '\0';
+	for (c = cbuf.data, shift = NULL; *c != '\0'; c++)
+		switch (*c) {
+		case '+':
+			*c = '&';
+			shift = c;
+			break;
+		case '-':
+			shift = NULL;
+			break;
+		case '/':
+			if (shift != NULL)
+				*c = ',';
+			break;
+		}
+	if (shift != NULL) {
+		*outbuf++ = '-';
+		*outbuf = '\0';
+	}
+	if (*(mbox + n - 1) == '*' || *(mbox + n - 1) == '%') {
+		*outbuf++ = *(mbox + n - 1);
+		*outbuf = '\0';
+	}
+
+	debug("conversion: '%s' -> '%s'\n", mbox, cbuf.data);
+
+	return cbuf.data;
+}
+
+/*
+ * Convert a mailbox name from the modified UTF-7 encoding, according to RFC
+ * 3501 Section 5.1.3.
+ */
+const char *reverse_conversion(const char *mbox)
+{
+	iconv_t cd;
+	char *inbuf, *outbuf;
+	size_t inlen, outlen;
+	char *c, *shift;
+	
+	buffer_check(&cbuf, strlen(mbox));
+	buffer_reset(&cbuf);
+	xstrncpy(cbuf.data, mbox, cbuf.size);
+	for (c = cbuf.data, shift = NULL; *c != '\0'; c++)
+		switch (*c) {
+		case '&':
+			*c = '+';
+			shift = c;
+			break;
+		case '-':
+			shift = NULL;
+			break;
+		case ',':
+			if (shift != NULL)
+				*c = '/';
+			break;
+		}
+
+	do {
+		inbuf = cbuf.data;
+		inlen = strlen(cbuf.data);
+
+		buffer_check(&nbuf, inlen);
+		buffer_reset(&nbuf);
+
+		outbuf = nbuf.data;
+		outlen = nbuf.size;
+
+		cd = iconv_open("", "UTF-7");
+		if (cd == (iconv_t)-1) {
+			error("converting mailbox name; %s\n", strerror(errno));
+			return mbox;
+		}
+		while (inlen > 0) {
+			if (iconv(cd, &inbuf, &inlen, &outbuf, &outlen) == -1) {
+				if (errno == E2BIG) {
+					buffer_check(&nbuf, nbuf.size * 2);
+					break;
+				} else {
+					error("converting mailbox name; %s\n",
+					    strerror(errno));
+					return mbox;
+				}
+			} else {
+				iconv(cd, NULL, NULL, &outbuf, &outlen);
+			}
+		}
+		iconv_close(cd);
+	} while (inlen > 0);
+
+	*outbuf = '\0';
+	for (c = nbuf.data; (c = strchr(c,'+')) != NULL; *c = '&');
+
+	debug("conversion: '%s' <- '%s'\n", mbox, nbuf.data);
+
 	return nbuf.data;
 }