---
 message/encodedword.ha | 73 ++++++++++++++++++++++++++++++++++++++++++
 message/header.ha      |  5 ++-
 2 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 message/encodedword.ha

diff --git a/message/encodedword.ha b/message/encodedword.ha
new file mode 100644
index 0000000..99c45bd
--- /dev/null
+++ b/message/encodedword.ha
@@ -0,0 +1,73 @@
+use encoding::base64;
+use regex;
+use strconv;
+use strings;
+
+let re_encoded_word_utf8: regex::regex = regex::regex { ... };
+
+@init fn init() void = {
+	re_encoded_word_utf8 = regex::compile(`=\?(utf|UTF)-8\?([bBqQ])\?([^?]+)\?=`)!;
+};
+
+@fini fn fini() void = {
+	regex::finish(&re_encoded_word_utf8);
+};
+
+fn decode_q_encoded_string(s: str) str = {
+	let result: []u8 = alloc([0...], len(s));
+	let bytes = strings::toutf8(s);
+	let j = 0z;
+	for (let i = 0z; i < len(s); i += 1) {
+		if (bytes[i] == '=' && i+2 < len(s)) {
+			i += 1;
+			const byte = match (strconv::stou8b(strings::sub(s, i, i+2), 16)) {
+			case let b: u8 => yield b;
+			case => yield '?': u8;
+			};
+			result[j] = byte;
+			i += 1;
+		} else if (bytes[i] == '_') {
+			result[j] = ' ';
+		} else {
+			result[j] = bytes[i];
+		};
+		j += 1;
+	};
+	return strings::fromutf8(result[0..j])!;
+};
+
+@test fn decode_q_encoded_string() void = {
+	assert(decode_q_encoded_string("M=C3=BCller") == "Müller");
+	assert(decode_q_encoded_string("B=C3=A9la_Bart=C3=B3k") == "Béla Bartók");
+	assert(decode_q_encoded_string("=F0=9F=98=8E") == "😎");
+};
+
+fn decode_encoded_words(line: str) str = {
+	for (let matches = regex::find(&re_encoded_word_utf8, line);
+			len(matches) == 4;
+			matches = regex::find(&re_encoded_word_utf8, line)) {
+		const matches = regex::find(&re_encoded_word_utf8, line);
+		// TODO: Handle charsets other than UTF-8
+		defer free(matches);
+		if (len(matches) != 4) {
+			return line;
+		};
+		switch (matches[2].content) {
+		case "B", "b" =>
+			const decoded_slice =
+				encoding::base64::decodestr(&encoding::base64::std_encoding, matches[3].content)!;
+			const decoded_string = strings::fromutf8(decoded_slice)!;
+			line = strings::replace(line, matches[0].content, decoded_string);
+		case "Q", "q" =>
+			line = strings::replace(line, matches[0].content, decode_q_encoded_string(matches[3].content));
+		case => true;
+		};
+	};
+	return line;
+};
+
+@test fn decode_encoded_words() void = {
+	assert(decode_encoded_words("=?UTF-8?Q?M=C3=B6ller?=") == "Möller");
+	assert(decode_encoded_words("=?UTF-8?B?5byg5LiJ?= <zhang.san@example.com>")
+		== "张三 <zhang.san@example.com>");
+};
diff --git a/message/header.ha b/message/header.ha
index cd35132..4d31298 100644
--- a/message/header.ha
+++ b/message/header.ha
@@ -101,7 +101,7 @@ export fn header_get(head: *header, key: str) str = {
 		if (map.key != key) {
 			continue;
 		};
-		return map.fields[len(map.fields) - 1].val;
+		return decode_encoded_words(map.fields[len(map.fields) - 1].val);
 	};
 
 	return "";
@@ -123,6 +123,9 @@ export fn header_get(head: *header, key: str) str = {
 	header_add(&head, "User-Agent", "Harriet");
 	assert(header_get(&head, "User-Agent") == "Harriet");
 
+	header_add(&head, "To", "=?UTF-8?Q?A._D=C3=BCrer?= <duerer@example.org>");
+	assert(header_get(&head, "To") == "A. Dürer <duerer@example.org>");
+
 	assert(header_get(&head, "foobar") == "");
 };
 
-- 
2.44.0

I'll need a few more things here before this patch is acceptable.

1. We need to be able to encode these, not just decode them
2. We need a test that the round-trip behavior works (and produces an
   email identical to the original)
3. To ease code review, please add the necessary RFC references into the
   commit message.

Thanks!