diff --git a/src/decrypt.rs b/src/decrypt.rs
index b3413bb65..457af6851 100644
--- a/src/decrypt.rs
+++ b/src/decrypt.rs
@@ -5,7 +5,7 @@ use std::collections::HashSet;
 use anyhow::{Context as _, Result};
 use mailparse::ParsedMail;
 
-use crate::aheader::{Aheader, EncryptPreference};
+use crate::aheader::Aheader;
 use crate::authres::handle_authres;
 use crate::authres::{self, DkimResults};
 use crate::contact::addr_cmp;
@@ -61,7 +61,6 @@ pub(crate) async fn prepare_decryption(
     mail: &ParsedMail<'_>,
     from: &str,
     message_time: i64,
-    is_thunderbird: bool,
 ) -> Result<DecryptionInfo> {
     if mail.headers.get_header(HeaderDef::ListPost).is_some() {
         if mail.headers.get_header(HeaderDef::Autocrypt).is_some() {
@@ -84,16 +83,10 @@ pub(crate) async fn prepare_decryption(
         });
     }
 
-    let mut autocrypt_header = Aheader::from_headers(from, &mail.headers)
+    let autocrypt_header = Aheader::from_headers(from, &mail.headers)
         .ok_or_log_msg(context, "Failed to parse Autocrypt header")
         .flatten();
 
-    if is_thunderbird {
-        if let Some(autocrypt_header) = &mut autocrypt_header {
-            autocrypt_header.prefer_encrypt = EncryptPreference::Mutual;
-        }
-    }
-
     let dkim_results = handle_authres(context, mail, from, message_time).await?;
 
     let peerstate = get_autocrypt_peerstate(
diff --git a/src/mimeparser.rs b/src/mimeparser.rs
index 2899a24f5..1b68b29de 100644
--- a/src/mimeparser.rs
+++ b/src/mimeparser.rs
@@ -216,16 +216,9 @@ impl MimeMessage {
         headers.remove("secure-join-fingerprint");
         headers.remove("chat-verified");
 
-        let is_thunderbird = if let Some(user_agent) = headers.get("user-agent") {
-            info!(context, "Detected thunderbird");
-            user_agent.contains("Thunderbird")
-        } else {
-            false
-        };
-
         let from = from.context("No from in message")?;
         let mut decryption_info =
-            prepare_decryption(context, &mail, &from.addr, message_time, is_thunderbird).await?;
+            prepare_decryption(context, &mail, &from.addr, message_time).await?;
 
         // Memory location for a possible decrypted message.
         let mut mail_raw = Vec::new();