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make encoding compliant with rfc 2047 #228

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9fbacd8
make encoding compliant with rfc 2047
Apr 1, 2026
fdcc3bb
Encode characters not allowed in atoms per RFC 2822
Apr 2, 2026
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28 changes: 25 additions & 3 deletions lib/mail/renderers/rfc_2822.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -156,8 +156,16 @@ defmodule Mail.Renderers.RFC2822 do
end
end

defp render_address({name, email}),
do: "#{encode_header_value(~s("#{name}"), :quoted_printable)} <#{validate_address(email)}>"
defp render_address({name, email}) do
address = validate_address(email)
encoded = encode_header_value(name, :quoted_printable)

if encoded == name do
~s("#{name}" <#{address}>)
else
"#{encoded} <#{address}>"
end
end

defp render_address(email), do: validate_address(email)

Expand Down Expand Up @@ -229,10 +237,24 @@ defmodule Mail.Renderers.RFC2822 do

defp wrap_encoded_words(value) do
:binary.split(value, "=\r\n", [:global])
|> Enum.map(fn chunk -> <<"=?UTF-8?Q?", chunk::binary, "?=">> end)
|> Enum.map(fn chunk ->
chunk = encode_encoded_word_text(chunk)
<<"=?UTF-8?Q?", chunk::binary, "?=">>
end)
|> Enum.join()
end

# Per RFC 2047 §5, encoded-words must be recognizable as atoms (RFC 2822 §3.2.4).
# Spaces become underscores per RFC 2047 §4.2(2).
# All other non-atext characters are QP-encoded.
defp encode_encoded_word_text(chunk) do
chunk
|> String.replace(" ", "_")
|> String.replace(~r/[^a-zA-Z0-9!#$%&'*+\-\/=?^_`{|}~]/, fn <<byte>> ->
"=" <> Base.encode16(<<byte>>)
end)
end

@doc """
Builds a RFC2822 timestamp from an Erlang timestamp

Expand Down
57 changes: 49 additions & 8 deletions test/mail/message_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -219,7 +219,7 @@ defmodule Mail.MessageTest do
|> Mail.put_subject(subject)
|> Mail.render()

encoded_subject = "=?UTF-8?Q?" <> Mail.Encoders.QuotedPrintable.encode(subject) <> "?="
encoded_subject = "=?UTF-8?Q?" <> encode_rfc2047(subject) <> "?="

assert String.contains?(txt, encoded_subject)
assert %Mail.Message{headers: %{"subject" => ^subject}} = Mail.Parsers.RFC2822.parse(txt)
Expand All @@ -244,14 +244,46 @@ defmodule Mail.MessageTest do
|> Mail.put_to(to)
|> Mail.render()

encoded_from =
~s(From: =?UTF-8?Q?"#{Mail.Encoders.QuotedPrintable.encode(elem(from, 0))}"?= <#{elem(from, 1)}>)

encoded_to =
~s(To: =?UTF-8?Q?"#{Mail.Encoders.QuotedPrintable.encode(elem(to, 0))}"?= <#{elem(to, 1)}>)
encoded_from = "From: =?UTF-8?Q?#{encode_rfc2047(elem(from, 0))}?= <#{elem(from, 1)}>"
encoded_to = "To: =?UTF-8?Q?#{encode_rfc2047(elem(to, 0))}?= <#{elem(to, 1)}>"

assert txt =~ encoded_from
assert txt =~ encoded_to

parsed = Mail.Parsers.RFC2822.parse(txt)
assert {elem(from, 0), elem(from, 1)} == parsed.headers["from"]
assert [{elem(to, 0), elem(to, 1)}] == parsed.headers["to"]
end

test "UTF-8 in addresses round-trips with spaces" do
from = {"Mäx Müstermann", "max@example.com"}

txt =
Mail.build()
|> Mail.put_from(from)
|> Mail.render()

refute txt =~ ~r/=\?UTF-8\?Q\?[^?]* [^?]*\?=/
parsed = Mail.Parsers.RFC2822.parse(txt)
assert from == parsed.headers["from"]
end

test "UTF-8 in addresses with comma in name" do
from = {"Max, Müstermänn", "max@example.com"}
to = {"Other User", "other@example.com"}

txt =
Mail.build()
|> Mail.put_from(from)
|> Mail.put_to(to)
|> Mail.render()

# Comma must be encoded as =2C, not literal, to avoid being parsed as recipient separator
refute txt =~ ~r/=\?UTF-8\?Q\?[^?]*,[^?]*\?=/
assert txt =~ "=2C"

parsed = Mail.Parsers.RFC2822.parse(txt)
assert from == parsed.headers["from"]
end

test "UTF-8 in other header" do
Expand All @@ -263,7 +295,7 @@ defmodule Mail.MessageTest do
|> Mail.render()

encoded_header_value =
"=?UTF-8?Q?" <> Mail.Encoders.QuotedPrintable.encode("READMEüä.md") <> "?="
"=?UTF-8?Q?" <> encode_rfc2047("READMEüä.md") <> "?="

assert String.contains?(message, encoded_header_value)

Expand All @@ -282,9 +314,18 @@ defmodule Mail.MessageTest do
|> Mail.render()

encoded_subject =
"=?UTF-8?Q?=C3=BCber alles=0Anew =3F=3D line some =D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C long line?="
"=?UTF-8?Q?=C3=BCber_alles=0Anew_=3F=3D_line_some_=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD?==?UTF-8?Q?=D1=8C-=D0=BE=D1=87=D0=B5=D0=BD=D1=8C_long_line?="

assert String.contains?(txt, encoded_subject)
assert %Mail.Message{headers: %{"subject" => ^subject}} = Mail.Parsers.RFC2822.parse(txt)
end

defp encode_rfc2047(string) do
string
|> Mail.Encoders.QuotedPrintable.encode()
|> String.replace(" ", "_")
|> String.replace(~r/[^a-zA-Z0-9!#$%&'*+\-\/=?^_`{|}~]/, fn <<byte>> ->
"=" <> Base.encode16(<<byte>>)
end)
end
end
10 changes: 5 additions & 5 deletions test/mail/renderers/rfc_2822_test.exs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,27 +52,27 @@ defmodule Mail.Renderers.RFC2822Test do

assert Mail.Renderers.RFC2822.render_header("Subject", [
"Hello World 😀"
]) == "Subject: =?UTF-8?Q?Hello World =F0=9F=98=80?="
]) == "Subject: =?UTF-8?Q?Hello_World_=F0=9F=98=80?="

assert Mail.Renderers.RFC2822.render_header("Subject", [
"Café résumé"
]) == "Subject: =?UTF-8?Q?Caf=C3=A9 r=C3=A9sum=C3=A9?="
]) == "Subject: =?UTF-8?Q?Caf=C3=A9_r=C3=A9sum=C3=A9?="

assert Mail.Renderers.RFC2822.render_header("Subject", [
"Hello 世界 World"
]) == "Subject: =?UTF-8?Q?Hello =E4=B8=96=E7=95=8C World?="
]) == "Subject: =?UTF-8?Q?Hello_=E4=B8=96=E7=95=8C_World?="

assert Mail.Renderers.RFC2822.render_header("Subject", [
"normal subject\r\nReply-To: cleverhacker@example.com"
]) == "Subject: =?UTF-8?Q?normal subject=0D=0AReply-To: cleverhacker@example.com?="
]) == "Subject: =?UTF-8?Q?normal_subject=0D=0AReply-To=3A_cleverhacker=40example=2Ecom?="

assert Mail.Renderers.RFC2822.render_header("Subject", [
"tabs\t\t and spaces"
]) == "Subject: tabs\t\t and spaces"

assert Mail.Renderers.RFC2822.render_header("Subject", [
"delete \x7f vertical tab \x0b"
]) == "Subject: =?UTF-8?Q?delete =7F vertical tab =0B?="
]) == "Subject: =?UTF-8?Q?delete_=7F_vertical_tab_=0B?="
end

test "address headers renders list of recipients" do
Expand Down
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