[pbs-devel] [PATCH proxmox 2/3] sendmail: encode non-ascii bodies as base64 to improve comptability
Shannon Sterz
s.sterz at proxmox.com
Tue Sep 2 16:27:16 CEST 2025
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 at 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 at example.com",
"Subject Linë",
- "Lorem Ipsum Dolor Sit\nAmet",
+ "Lorem Ipsum Dolor Sit\nAmët",
)
.with_recipient_and_name("Receiver Näme", "receiver at 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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