diff --git a/Cargo.lock b/Cargo.lock
index e8b500f..1b7c730 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -103,9 +103,9 @@ checksum = "76a2e8124351fda1ef8aaaa3bbd7ebbcb486bbcd4225aca0aa0d84bb2db8fecb"
 
 [[package]]
 name = "arrayvec"
-version = "0.7.6"
+version = "0.7.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7c02d123df017efcdfbd739ef81735b36c5ba83ec3c59c80a9d7ecc718f92e50"
+checksum = "f02882884d3e1bc524fb12c79f107f6ad0e1cfd498c536ffb494301740995dfe"
 
 [[package]]
 name = "assert-json-diff"
@@ -384,9 +384,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.2.64"
+version = "1.2.65"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "dad887fd958be91b5098c0248def011f4523ab786cd411be668777e55063501f"
+checksum = "e228eec9be7c17ccb640b59b36a5cd805ea2a564a4c5e162c2f659fea30d3b96"
 dependencies = [
  "find-msvc-tools",
  "jobserver",
@@ -1487,9 +1487,9 @@ dependencies = [
 
 [[package]]
 name = "log"
-version = "0.4.32"
+version = "0.4.33"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "953f07c43838f8e6f9758cab68bf5bed85465e7587ebe0b823f1bcd81978ad3a"
+checksum = "0ceec5bc11778974d1bcb055b18002eba7f4b3518b6a0081b3af5f21666da9ad"
 
 [[package]]
 name = "mail-builder"
@@ -1499,9 +1499,9 @@ checksum = "900998f307338c4013a28ab14d760b784067324b164448c6d98a89e44810473b"
 
 [[package]]
 name = "mail-parser"
-version = "0.11.3"
+version = "0.11.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8a2420e9ce11c2b0583ca97ddff7ab2398c8a613154e9b72e3bafdbf767f1d7"
+checksum = "f2c0e7e0704500930be5b6c629f30d23fd1dde4d1800e138e04b3fa302e64d51"
 dependencies = [
  "hashify",
 ]
diff --git a/src/dav/discover.rs b/src/dav/discover.rs
index eab0d4f..d87f851 100644
--- a/src/dav/discover.rs
+++ b/src/dav/discover.rs
@@ -131,6 +131,10 @@ fn try_treat_url_as_home_or_collection(
         {
             return Ok(None);
         }
+        Err(DiscoveryError::Transport(JmapError::Malformed(_)))
+        | Err(DiscoveryError::Transport(JmapError::RetriesExhausted(_))) => {
+            return Ok(None);
+        }
         Err(e) => return Err(e),
     };
     if collections.is_empty() {
@@ -158,7 +162,7 @@ fn resolve_principal_url(
         Err(JmapError::HttpStatus { status, .. }) if (400..600).contains(&status) => {
             return Ok(None);
         }
-        Err(JmapError::RetriesExhausted(_)) => return Ok(None),
+        Err(JmapError::RetriesExhausted(_)) | Err(JmapError::Malformed(_)) => return Ok(None),
         Err(e) => return Err(DiscoveryError::Transport(e)),
     };
     let final_url = ms.final_url.clone();
@@ -186,7 +190,7 @@ fn try_via_principal(
         Err(JmapError::HttpStatus { status, .. }) if (400..600).contains(&status) => {
             return Ok(None);
         }
-        Err(JmapError::RetriesExhausted(_)) => return Ok(None),
+        Err(JmapError::RetriesExhausted(_)) | Err(JmapError::Malformed(_)) => return Ok(None),
         Err(e) => return Err(DiscoveryError::Transport(e)),
     };
     let first_final_url = first_ms.final_url.clone();
@@ -217,7 +221,9 @@ fn try_via_principal(
                 Err(JmapError::HttpStatus { status, .. }) if (400..600).contains(&status) => {
                     return Ok(None);
                 }
-                Err(JmapError::RetriesExhausted(_)) => return Ok(None),
+                Err(JmapError::RetriesExhausted(_)) | Err(JmapError::Malformed(_)) => {
+                    return Ok(None)
+                }
                 Err(e) => return Err(DiscoveryError::Transport(e)),
             };
         let principal_after_redirect = home_ms.final_url.clone();
diff --git a/tests/seed_smoke.rs b/tests/seed_smoke.rs
index fba196f..5475b25 100644
--- a/tests/seed_smoke.rs
+++ b/tests/seed_smoke.rs
@@ -14,6 +14,7 @@ use serde_json::{Value, json};
 
 const CORE: &str = "urn:ietf:params:jmap:core";
 const MAIL: &str = "urn:ietf:params:jmap:mail";
+const SUBMISSION: &str = "urn:ietf:params:jmap:submission";
 const SIEVE: &str = "urn:ietf:params:jmap:sieve";
 const CONTACTS: &str = "urn:ietf:params:jmap:contacts";
 const CALENDARS: &str = "urn:ietf:params:jmap:calendars";
@@ -110,7 +111,7 @@ fn verify_account(label: &str, user: &Jmap, account_id: &str, s: &SeedStats) {
 
     let identities = user
         .call(
-            &[CORE, MAIL],
+            &[CORE, SUBMISSION],
             "Identity/get",
             account_id,
             json!({ "properties": ["id", "name"] }),
diff --git a/tests/seeder/data.rs b/tests/seeder/data.rs
index c693059..e7ee39c 100644
--- a/tests/seeder/data.rs
+++ b/tests/seeder/data.rs
@@ -35,10 +35,11 @@ pub fn load_mbox(limit: usize) -> SeedResult<Vec<MboxMessage>> {
     for item in MessageIterator::new(reader) {
         let message = item.map_err(|e| SeedError::Resource(format!("mbox parse: {e}")))?;
         let received_at = message.internal_date() as i64;
-        out.push(MboxMessage {
-            raw: message.unwrap_contents(),
-            received_at,
-        });
+        let raw = message.unwrap_contents();
+        if !starts_with_header(&raw) {
+            continue;
+        }
+        out.push(MboxMessage { raw, received_at });
         if out.len() >= limit {
             break;
         }
@@ -49,6 +50,27 @@ pub fn load_mbox(limit: usize) -> SeedResult<Vec<MboxMessage>> {
     Ok(out)
 }
 
+fn starts_with_header(raw: &[u8]) -> bool {
+    let mut rest = raw;
+    if rest.starts_with(b"From ") {
+        match rest.iter().position(|b| *b == b'\n') {
+            Some(nl) => rest = &rest[nl + 1..],
+            None => return false,
+        }
+    }
+    let line_end = rest.iter().position(|b| *b == b'\n').unwrap_or(rest.len());
+    let line = &rest[..line_end];
+    let Some(colon) = line.iter().position(|b| *b == b':') else {
+        return false;
+    };
+    if colon == 0 {
+        return false;
+    }
+    line[..colon]
+        .iter()
+        .all(|b| b.is_ascii_graphic() && *b != b':')
+}
+
 fn read_dir_sorted(sub: &str, ext: &str) -> SeedResult<Vec<PathBuf>> {
     let dir = resources_dir().join(sub);
     let mut paths: Vec<PathBuf> = std::fs::read_dir(&dir)?