diff --git a/crates/core/src/database/auth.rs b/crates/core/src/database/auth.rs
index fcd34be..4ced643 100644
--- a/crates/core/src/database/auth.rs
+++ b/crates/core/src/database/auth.rs
@@ -101,13 +101,9 @@ impl DataManager {
             permissions: FinePermission::from_bits(get!(x->7(i32)) as u32).unwrap(),
             is_verified: get!(x->8(i32)) as i8 == 1,
             notification_count: {
-                let x = get!(x->9(i32));
-                if x > (usize::MAX - 1000) as i32 {
-                    // we're a little too close to the maximum count, clearly something's gone wrong
-                    0
-                } else {
-                    x as usize
-                }
+                let x = get!(x->9(i32)) as usize;
+                // we're a little too close to the maximum count, clearly something's gone wrong
+                if x > usize::MAX - 1000 { 0 } else { x }
             },
             follower_count: get!(x->10(i32)) as usize,
             following_count: get!(x->11(i32)) as usize,
@@ -116,12 +112,8 @@ impl DataManager {
             recovery_codes: serde_json::from_str(&get!(x->14(String)).to_string()).unwrap(),
             post_count: get!(x->15(i32)) as usize,
             request_count: {
-                let x = get!(x->16(i32));
-                if x > (usize::MAX - 1000) as i32 {
-                    0
-                } else {
-                    x as usize
-                }
+                let x = get!(x->16(i32)) as usize;
+                if x > usize::MAX - 1000 { 0 } else { x }
             },
             connections: serde_json::from_str(&get!(x->17(String)).to_string()).unwrap(),
             stripe_id: get!(x->18(String)),
diff --git a/crates/core/src/database/drivers/sql/version_migrations.sql b/crates/core/src/database/drivers/sql/version_migrations.sql
index 1988e63..c101e7d 100644
--- a/crates/core/src/database/drivers/sql/version_migrations.sql
+++ b/crates/core/src/database/drivers/sql/version_migrations.sql
@@ -9,3 +9,7 @@ ADD COLUMN IF NOT EXISTS is_deactivated INT DEFAULT 0;
 -- apps storage_capacity
 ALTER TABLE apps
 ADD COLUMN IF NOT EXISTS storage_capacity TEXT DEFAULT '"Tier1"';
+
+-- letters replying_to
+ALTER TABLE letters
+ADD COLUMN IF NOT EXISTS replying_to TEXT DEFAULT 0;
diff --git a/crates/core/src/database/letters.rs b/crates/core/src/database/letters.rs
index 32f8187..fe9bbac 100644
--- a/crates/core/src/database/letters.rs
+++ b/crates/core/src/database/letters.rs
@@ -13,6 +13,7 @@ impl DataManager {
             subject: get!(x->4(String)),
             content: get!(x->5(String)),
             read_by: serde_json::from_str(&get!(x->6(String))).unwrap(),
+            replying_to: get!(x->7(i32)) as usize,
         }
     }
 
@@ -66,6 +67,30 @@ impl DataManager {
         Ok(res.unwrap())
     }
 
+    /// Get all letters which are replying to the given letter.
+    ///
+    /// # Arguments
+    /// * `id` - the ID of the letter to fetch letters for
+    pub async fn get_letters_by_replying_to(&self, id: usize) -> Result<Vec<Letter>> {
+        let conn = match self.0.connect().await {
+            Ok(c) => c,
+            Err(e) => return Err(Error::DatabaseConnection(e.to_string())),
+        };
+
+        let res = query_rows!(
+            &conn,
+            "SELECT * FROM letters WHERE replying_to = $1 ORDER BY created DESC",
+            &[&(id as i64)],
+            |x| { Self::get_letter_from_row(x) }
+        );
+
+        if res.is_err() {
+            return Err(Error::GeneralNotFound("letter".to_string()));
+        }
+
+        Ok(res.unwrap())
+    }
+
     /// Create a new letter in the database.
     ///
     /// # Arguments
@@ -92,7 +117,7 @@ impl DataManager {
 
         let res = execute!(
             &conn,
-            "INSERT INTO letters VALUES ($1, $2, $3, $4, $5, $6, $7)",
+            "INSERT INTO letters VALUES ($1, $2, $3, $4, $5, $6, $7, $8)",
             params![
                 &(data.id as i64),
                 &(data.created as i64),
@@ -101,6 +126,7 @@ impl DataManager {
                 &data.subject,
                 &data.content,
                 &serde_json::to_string(&data.read_by).unwrap(),
+                &(data.replying_to as i64)
             ]
         );
 
diff --git a/crates/core/src/model/mail.rs b/crates/core/src/model/mail.rs
index 849aaae..8336821 100644
--- a/crates/core/src/model/mail.rs
+++ b/crates/core/src/model/mail.rs
@@ -17,11 +17,19 @@ pub struct Letter {
     /// This field can be updated by anyone in the letter's `receivers` field.
     /// Other fields in the letter can only be updated by the letter's `owner`.
     pub read_by: Vec<usize>,
+    /// The ID of the letter this letter is replying to.
+    pub replying_to: usize,
 }
 
 impl Letter {
     /// Create a new [`Letter`].
-    pub fn new(owner: usize, receivers: Vec<usize>, subject: String, content: String) -> Self {
+    pub fn new(
+        owner: usize,
+        receivers: Vec<usize>,
+        subject: String,
+        content: String,
+        replying_to: usize,
+    ) -> Self {
         Self {
             id: Snowflake::new().to_string().parse::<usize>().unwrap(),
             created: unix_epoch_timestamp(),
@@ -30,6 +38,7 @@ impl Letter {
             subject,
             content,
             read_by: Vec::new(),
+            replying_to,
         }
     }
 }