diff --git a/Cargo.lock b/Cargo.lock
index cc51987..2967628 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -235,6 +235,16 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "email-encoding"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "75b91dddc343e7eaa27f9764e5bffe57370d957017fdd75244f5045e829a8441"
+dependencies = [
+ "base64",
+ "memchr 2.4.1",
+]
+
 [[package]]
 name = "encoding_rs"
 version = "0.8.30"
@@ -605,11 +615,12 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "lettre"
-version = "0.10.0-rc.4"
+version = "0.10.0-rc.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "71d8da8f34d086b081c9cc3b57d3bb3b51d16fc06b5c848a188e2f14d58ac2a5"
+checksum = "2f6c70001f7ee6c93b6687a06607c7a38f9a7ae460139a496c23da21e95bc289"
 dependencies = [
  "base64",
+ "email-encoding",
  "fastrand",
  "futures-util",
  "hostname",
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 51d2f2c..fecd793 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -10,7 +10,7 @@ notmuch-backend = ["notmuch", "maildir-backend"]
 default = ["imap-backend", "maildir-backend", "notmuch-backend"]
 
 [dependencies]
-lettre = { version = "0.10.0-rc.1", features = ["serde"] }
+lettre = { version = "0.10.0-rc.6", features = ["serde"] }
 log = "0.4.14"
 mailparse = "0.13.6"
 serde = { version = "1.0.118", features = ["derive"] }