[pbs-devel] [PATCH proxmox 0/3] improve mail compatability

[pbs-devel] [PATCH proxmox 0/3] improve mail compatability

[Shannon Sterz]

this series tries to improve compatability with more mail servers. this
is done in three ways:

- patch 1: base64 encode filenames of attachments
- patch 2: check whether the html or text bodies of an email are ascii
  only. if they are, we can safely declare 7bit encoding which should be
  more broadly compatability than the previous 8bit encoding. if the
  text is not ascii only, encode it as base64 and declare base64
  encoding.
- patch 3: splits the Content-Disposition header of attached files over
  two lines, to avoid longer files possibly triggering a line length
  limit.

this should specifically make it possible to support mail servers that
don't support SMTPUTF8, as now no part of the header or body should
contain plain utf8 characters directly.

i tested these patches against the following mail clients:

- bluemind
- Thunderbird
- aerc
- canary [1]
- iOS Mail app
- gmail.com
- outlook.com

all of them seemed to receive the email and display it properly (note
that aerc prefers the TXT part of the mime alternative parts even if the
html part should be preferred, due to being a terminal based mua).

[1]: https://canarymail.io/

Shannon Sterz (3):
  sendmail: encode non-ascii filenames to improve compatability
  sendmail: encode non-ascii bodies as base64 to improve comptability
  sendmail: break content disposition headers for attachments

 proxmox-sendmail/src/lib.rs | 193 +++++++++++++++++++++++++++---------
 1 file changed, 147 insertions(+), 46 deletions(-)

--
2.47.2



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[pbs-devel] [PATCH proxmox 1/3] sendmail: encode non-ascii filenames to improve compatability

[Shannon Sterz]

otherwise some mail servers that do not support utf8 properly mail not
accept the email.

Signed-off-by: Shannon Sterz <s.sterz@proxmox.com>
---
 proxmox-sendmail/src/lib.rs | 95 ++++++++++++++++++++++++++++++++++---
 1 file changed, 89 insertions(+), 6 deletions(-)

diff --git a/proxmox-sendmail/src/lib.rs b/proxmox-sendmail/src/lib.rs
index 053fc98e..ebbcfe86 100644
--- a/proxmox-sendmail/src/lib.rs
+++ b/proxmox-sendmail/src/lib.rs
@@ -81,18 +81,23 @@ impl Attachment<'_> {
 
         let mut attachment = String::new();
 
+        let encoded_filename = if self.filename.is_ascii() {
+            &self.filename
+        } else {
+            &format!("=?utf-8?B?{}?=", proxmox_base64::encode(&self.filename))
+        };
+
         let _ = writeln!(attachment, "\n--{file_boundary}");
         let _ = writeln!(
             attachment,
-            "Content-Type: {}; name=\"{}\"",
-            self.mime, self.filename
+            "Content-Type: {}; name=\"{encoded_filename}\"",
+            self.mime,
         );
 
         // both `filename` and `filename*` are included for additional compatability
         let _ = writeln!(
             attachment,
-            "Content-Disposition: attachment; filename=\"{}\"; filename*=UTF-8''{}",
-            self.filename,
+            "Content-Disposition: attachment; filename=\"{encoded_filename}\"; filename*=UTF-8''{}",
             utf8_percent_encode(&self.filename, RFC5987SET)
         );
         attachment.push_str("Content-Transfer-Encoding: base64\n\n");
@@ -804,8 +809,8 @@ Content-Transfer-Encoding: base64
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
 3q2+796tvu8=
 ------_=_NextPart_001_1732806251
-Content-Type: image/bmp; name="🐄💀.bin"
-Content-Disposition: attachment; filename="🐄💀.bin"; filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
+Content-Type: image/bmp; name="=?utf-8?B?8J+QhPCfkoAuYmlu?="
+Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?="; filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
@@ -855,4 +860,82 @@ Content-Transfer-Encoding: 8bit
 ------_=_NextPart_002_1718977850--"#,
         );
     }
+
+    #[test]
+    fn multipart_plain_text_html_alternative_attachments_ascii_compat() {
+        let bin: [u8; 62] = [
+            0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad,
+            0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad,
+            0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad,
+            0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef, 0xde, 0xad,
+            0xbe, 0xef, 0xde, 0xad, 0xbe, 0xef,
+        ];
+
+        let mail = Mail::new(
+            "Sender Näme",
+            "from@example.com",
+            "Subject Linë",
+            "Lorem Ipsum Dolor Sit\nAmet",
+        )
+        .with_recipient_and_name("Receiver Näme", "receiver@example.com")
+        .with_attachment("deadbeef.bin", "application/octet-stream", &bin)
+        .with_attachment("🐄💀.bin", "image/bmp", &bin)
+        .with_html_alt("<html lang=\"de-at\"><head></head><body>\n\t<pre>\n\t\tLorem Ipsum Dolor Sit Amet\n\t</pre>\n</body></html>");
+
+        let body = mail.format_mail(1732806251).expect("could not format mail");
+
+        assert!(body.is_ascii());
+
+        assert_lines_equal_ignore_date(
+            &body,
+            r#"Content-Type: multipart/mixed;
+	boundary="----_=_NextPart_001_1732806251"
+MIME-Version: 1.0
+Subject: =?utf-8?B?U3ViamVjdCBMaW7Dqw==?=
+From: =?utf-8?B?U2VuZGVyIE7DpG1l?= <from@example.com>
+To: =?utf-8?B?UmVjZWl2ZXIgTsOkbWU=?= <receiver@example.com>
+Date: Thu, 28 Nov 2024 16:04:11 +0100
+Auto-Submitted: auto-generated;
+
+This is a multi-part message in MIME format.
+
+------_=_NextPart_001_1732806251
+Content-Type: multipart/alternative; boundary="----_=_NextPart_002_1732806251"
+MIME-Version: 1.0
+
+------_=_NextPart_002_1732806251
+Content-Type: text/plain;
+	charset="UTF-8"
+Content-Transfer-Encoding: 8bit
+
+Lorem Ipsum Dolor Sit
+Amet
+------_=_NextPart_002_1732806251
+Content-Type: text/html;
+	charset="UTF-8"
+Content-Transfer-Encoding: 8bit
+
+<html lang="de-at"><head></head><body>
+	<pre>
+		Lorem Ipsum Dolor Sit Amet
+	</pre>
+</body></html>
+------_=_NextPart_002_1732806251--
+------_=_NextPart_001_1732806251
+Content-Type: application/octet-stream; name="deadbeef.bin"
+Content-Disposition: attachment; filename="deadbeef.bin"; filename*=UTF-8''deadbeef.bin
+Content-Transfer-Encoding: base64
+
+3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
+3q2+796tvu8=
+------_=_NextPart_001_1732806251
+Content-Type: image/bmp; name="=?utf-8?B?8J+QhPCfkoAuYmlu?="
+Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?="; filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
+Content-Transfer-Encoding: base64
+
+3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
+3q2+796tvu8=
+------_=_NextPart_001_1732806251--"#,
+        )
+    }
 }
-- 
2.47.2



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[pbs-devel] [PATCH proxmox 2/3] sendmail: encode non-ascii bodies as base64 to improve comptability

[Shannon Sterz]

and use 7bit encoding otherwise. this should further improve
compatability with older mail servers that don't really handle 8bit
utf8 bodies properly. by base64 encoding the bodies that require it
and declaring 7bit ascii compatability otherwise, this should work
around compatability constraints.

Signed-off-by: Shannon Sterz <s.sterz@proxmox.com>
---
 proxmox-sendmail/src/lib.rs | 111 ++++++++++++++++++++----------------
 1 file changed, 62 insertions(+), 49 deletions(-)

diff --git a/proxmox-sendmail/src/lib.rs b/proxmox-sendmail/src/lib.rs
index ebbcfe86..fb201007 100644
--- a/proxmox-sendmail/src/lib.rs
+++ b/proxmox-sendmail/src/lib.rs
@@ -41,6 +41,24 @@ const RFC5987SET: &AsciiSet = &CONTROLS
     .add(b'{')
     .add(b'}');
 
+// base64 encode and hard-wrap the base64 encoded string every 72 characters. this improves
+// compatibility.
+fn encode_base64_formatted<T: AsRef<[u8]>>(raw: T) -> String {
+    proxmox_base64::encode(raw)
+        .chars()
+        .enumerate()
+        .flat_map(|(i, c)| {
+            if i != 0 && i % 72 == 0 {
+                Some('\n')
+            } else {
+                None
+            }
+            .into_iter()
+            .chain(std::iter::once(c))
+        })
+        .collect::<String>()
+}
+
 struct Recipient {
     name: Option<String>,
     email: String,
@@ -100,25 +118,9 @@ impl Attachment<'_> {
             "Content-Disposition: attachment; filename=\"{encoded_filename}\"; filename*=UTF-8''{}",
             utf8_percent_encode(&self.filename, RFC5987SET)
         );
-        attachment.push_str("Content-Transfer-Encoding: base64\n\n");
 
-        // base64 encode the attachment and hard-wrap the base64 encoded string every 72
-        // characters. this improves compatability.
-        attachment.push_str(
-            &proxmox_base64::encode(self.content)
-                .chars()
-                .enumerate()
-                .flat_map(|(i, c)| {
-                    if i != 0 && i % 72 == 0 {
-                        Some('\n')
-                    } else {
-                        None
-                    }
-                    .into_iter()
-                    .chain(std::iter::once(c))
-                })
-                .collect::<String>(),
-        );
+        attachment.push_str("Content-Transfer-Encoding: base64\n\n");
+        attachment.push_str(&encode_base64_formatted(self.content));
 
         attachment
     }
@@ -400,7 +402,11 @@ impl<'a> Mail<'a> {
             header.push_str("Content-Type: multipart/alternative;\n");
             writeln!(header, "\tboundary=\"{html_boundary}\"")?;
             header.push_str("MIME-Version: 1.0\n");
-        } else if !self.subject.is_ascii() || !self.mail_author.is_ascii() || encoded_to {
+        } else if !self.subject.is_ascii()
+            || !self.mail_author.is_ascii()
+            || !self.body_txt.is_ascii()
+            || encoded_to
+        {
             header.push_str("MIME-Version: 1.0\n");
         }
 
@@ -475,15 +481,28 @@ impl<'a> Mail<'a> {
 
         body.push_str("Content-Type: text/plain;\n");
         body.push_str("\tcharset=\"UTF-8\"\n");
-        body.push_str("Content-Transfer-Encoding: 8bit\n\n");
-        body.push_str(&self.body_txt);
+
+        if self.body_txt.is_ascii() {
+            body.push_str("Content-Transfer-Encoding: 7bit\n\n");
+            body.push_str(&self.body_txt);
+        } else {
+            body.push_str("Content-Transfer-Encoding: base64\n\n");
+            body.push_str(&encode_base64_formatted(&self.body_txt));
+        }
 
         if let Some(html) = &self.body_html {
             writeln!(body, "\n--{html_boundary}")?;
             body.push_str("Content-Type: text/html;\n");
             body.push_str("\tcharset=\"UTF-8\"\n");
-            body.push_str("Content-Transfer-Encoding: 8bit\n\n");
-            body.push_str(html);
+
+            if html.is_ascii() {
+                body.push_str("Content-Transfer-Encoding: 7bit\n\n");
+                body.push_str(html);
+            } else {
+                body.push_str("Content-Transfer-Encoding: base64\n\n");
+                body.push_str(&encode_base64_formatted(html));
+            }
+
             write!(body, "\n--{html_boundary}--")?;
         }
 
@@ -547,7 +566,7 @@ Date: Thu, 01 Jan 1970 01:00:00 +0100
 Auto-Submitted: auto-generated;
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 This is just ascii text.
 Nothing too special."#,
@@ -577,7 +596,7 @@ Date: Thu, 01 Jan 1970 01:00:00 +0100
 Auto-Submitted: auto-generated;
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 This is just ascii text.
 Nothing too special."#,
@@ -609,7 +628,7 @@ Date: Thu, 01 Jan 1970 01:00:00 +0100
 Auto-Submitted: auto-generated;
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 This is just ascii text.
 Nothing too special."#,
@@ -638,12 +657,10 @@ Date: Thu, 28 Nov 2024 16:04:11 +0100
 Auto-Submitted: auto-generated;
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: base64
 
-This utf-8 email should handle emojis
-🧑📧
-and weird german characters: öäüß
-and more."#,
+VGhpcyB1dGYtOCBlbWFpbCBzaG91bGQgaGFuZGxlIGVtb2ppcwrwn6eR8J+TpwphbmQgd2Vp
+cmQgZ2VybWFuIGNoYXJhY3RlcnM6IMO2w6TDvMOfCmFuZCBtb3JlLg=="#,
         )
     }
 
@@ -674,14 +691,14 @@ This is a multi-part message in MIME format.
 ------_=_NextPart_002_1732806251
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 Lorem Ipsum Dolor Sit
 Amet
 ------_=_NextPart_002_1732806251
 Content-Type: text/html;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 <html lang="de-at"><head></head><body>
 	<pre>
@@ -728,7 +745,7 @@ This is a multi-part message in MIME format.
 ------_=_NextPart_001_1732806251
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 Lorem Ipsum Dolor Sit
 Amet
@@ -786,14 +803,14 @@ MIME-Version: 1.0
 ------_=_NextPart_002_1732806251
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 Lorem Ipsum Dolor Sit
 Amet
 ------_=_NextPart_002_1732806251
 Content-Type: text/html;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 <html lang="de-at"><head></head><body>
 	<pre>
@@ -848,13 +865,13 @@ This is a multi-part message in MIME format.
 ------_=_NextPart_002_1718977850
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 This is the plain body
 ------_=_NextPart_002_1718977850
 Content-Type: text/html;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: 7bit
 
 <body>This is the HTML body</body>
 ------_=_NextPart_002_1718977850--"#,
@@ -875,12 +892,12 @@ Content-Transfer-Encoding: 8bit
             "Sender Näme",
             "from@example.com",
             "Subject Linë",
-            "Lorem Ipsum Dolor Sit\nAmet",
+            "Lorem Ipsum Dolor Sit\nAmët",
         )
         .with_recipient_and_name("Receiver Näme", "receiver@example.com")
         .with_attachment("deadbeef.bin", "application/octet-stream", &bin)
         .with_attachment("🐄💀.bin", "image/bmp", &bin)
-        .with_html_alt("<html lang=\"de-at\"><head></head><body>\n\t<pre>\n\t\tLorem Ipsum Dolor Sit Amet\n\t</pre>\n</body></html>");
+        .with_html_alt("<html lang=\"de-at\"><head></head><body>\n\t<pre>\n\t\tLorem Ipsum Dölor Sit Amet\n\t</pre>\n</body></html>");
 
         let body = mail.format_mail(1732806251).expect("could not format mail");
 
@@ -906,20 +923,16 @@ MIME-Version: 1.0
 ------_=_NextPart_002_1732806251
 Content-Type: text/plain;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: base64
 
-Lorem Ipsum Dolor Sit
-Amet
+TG9yZW0gSXBzdW0gRG9sb3IgU2l0CkFtw6t0
 ------_=_NextPart_002_1732806251
 Content-Type: text/html;
 	charset="UTF-8"
-Content-Transfer-Encoding: 8bit
+Content-Transfer-Encoding: base64
 
-<html lang="de-at"><head></head><body>
-	<pre>
-		Lorem Ipsum Dolor Sit Amet
-	</pre>
-</body></html>
+PGh0bWwgbGFuZz0iZGUtYXQiPjxoZWFkPjwvaGVhZD48Ym9keT4KCTxwcmU+CgkJTG9yZW0g
+SXBzdW0gRMO2bG9yIFNpdCBBbWV0Cgk8L3ByZT4KPC9ib2R5PjwvaHRtbD4=
 ------_=_NextPart_002_1732806251--
 ------_=_NextPart_001_1732806251
 Content-Type: application/octet-stream; name="deadbeef.bin"
-- 
2.47.2



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[pbs-devel] [PATCH proxmox 3/3] sendmail: break content disposition headers for attachments

[Shannon Sterz]

this should make it easier to accomodate longer filenames, as line
lengths in emails are constraint.

Signed-off-by: Shannon Sterz <s.sterz@proxmox.com>
---
 proxmox-sendmail/src/lib.rs | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/proxmox-sendmail/src/lib.rs b/proxmox-sendmail/src/lib.rs
index fb201007..1c5daf0f 100644
--- a/proxmox-sendmail/src/lib.rs
+++ b/proxmox-sendmail/src/lib.rs
@@ -115,7 +115,7 @@ impl Attachment<'_> {
         // both `filename` and `filename*` are included for additional compatability
         let _ = writeln!(
             attachment,
-            "Content-Disposition: attachment; filename=\"{encoded_filename}\"; filename*=UTF-8''{}",
+            "Content-Disposition: attachment; filename=\"{encoded_filename}\";\n\tfilename*=UTF-8''{}",
             utf8_percent_encode(&self.filename, RFC5987SET)
         );
 
@@ -751,7 +751,8 @@ Lorem Ipsum Dolor Sit
 Amet
 ------_=_NextPart_001_1732806251
 Content-Type: application/octet-stream; name="deadbeef.bin"
-Content-Disposition: attachment; filename="deadbeef.bin"; filename*=UTF-8''deadbeef.bin
+Content-Disposition: attachment; filename="deadbeef.bin";
+	filename*=UTF-8''deadbeef.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
@@ -820,14 +821,16 @@ Content-Transfer-Encoding: 7bit
 ------_=_NextPart_002_1732806251--
 ------_=_NextPart_001_1732806251
 Content-Type: application/octet-stream; name="deadbeef.bin"
-Content-Disposition: attachment; filename="deadbeef.bin"; filename*=UTF-8''deadbeef.bin
+Content-Disposition: attachment; filename="deadbeef.bin";
+	filename*=UTF-8''deadbeef.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
 3q2+796tvu8=
 ------_=_NextPart_001_1732806251
 Content-Type: image/bmp; name="=?utf-8?B?8J+QhPCfkoAuYmlu?="
-Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?="; filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
+Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?=";
+	filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
@@ -936,14 +939,16 @@ SXBzdW0gRMO2bG9yIFNpdCBBbWV0Cgk8L3ByZT4KPC9ib2R5PjwvaHRtbD4=
 ------_=_NextPart_002_1732806251--
 ------_=_NextPart_001_1732806251
 Content-Type: application/octet-stream; name="deadbeef.bin"
-Content-Disposition: attachment; filename="deadbeef.bin"; filename*=UTF-8''deadbeef.bin
+Content-Disposition: attachment; filename="deadbeef.bin";
+	filename*=UTF-8''deadbeef.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
 3q2+796tvu8=
 ------_=_NextPart_001_1732806251
 Content-Type: image/bmp; name="=?utf-8?B?8J+QhPCfkoAuYmlu?="
-Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?="; filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
+Content-Disposition: attachment; filename="=?utf-8?B?8J+QhPCfkoAuYmlu?=";
+	filename*=UTF-8''%F0%9F%90%84%F0%9F%92%80.bin
 Content-Transfer-Encoding: base64
 
 3q2+796tvu/erb7v3q3erb7v3q2+796tvu/erd6tvu/erb7v3q2+796t3q2+796tvu/erb7v
-- 
2.47.2



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