diff --git a/app/models.py b/app/models.py
index da6788a..2fe5847 100644
--- a/app/models.py
+++ b/app/models.py
@@ -327,7 +327,7 @@ class SystemSetting(db.Model):
 
     id          = db.Column(db.Integer, primary_key=True)
     key         = db.Column(db.String(100), unique=True, nullable=False, index=True)
-    value       = db.Column(db.String(500), nullable=False)
+    value       = db.Column(db.Text, nullable=False)
     description = db.Column(db.String(256))
     updated_at  = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
 
diff --git a/migrations/versions/004_widen_system_setting_value.py b/migrations/versions/004_widen_system_setting_value.py
new file mode 100644
index 0000000..e4fa9d5
--- /dev/null
+++ b/migrations/versions/004_widen_system_setting_value.py
@@ -0,0 +1,55 @@
+"""Widen system_settings value from VARCHAR(500) to TEXT
+
+Revision ID: 004_widen_system_setting_value
+Revises: 003_render_comments
+Create Date: 2026-04-17
+
+Rationale
+---------
+SystemSetting.value was VARCHAR(500), which is sufficient for short config
+values but overflows when the email_ingested_message_ids key accumulates
+multiple Outlook Message-IDs.  A single Outlook Message-ID can be ~100 chars,
+so even a modest backlog of 6–7 messages exceeds the 500-byte limit, causing:
+
+    pymysql.err.DataError: (1406, "Data too long for column 'value' at row 1")
+
+TEXT (up to 65,535 bytes) is the correct type for any value store that can
+hold accumulated lists or free-form strings of unbounded length.  This mirrors
+the same fix applied to ticket_history in migration 001.
+
+Apply
+-----
+    flask db upgrade
+
+Rollback
+--------
+    flask db downgrade
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+revision = '004_widen_system_setting_value'
+down_revision = '003_render_comments'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table('system_settings', schema=None) as batch_op:
+        batch_op.alter_column(
+            'value',
+            existing_type=sa.String(length=500),
+            type_=sa.Text(),
+            existing_nullable=False,
+        )
+
+
+def downgrade():
+    with op.batch_alter_table('system_settings', schema=None) as batch_op:
+        batch_op.alter_column(
+            'value',
+            existing_type=sa.Text(),
+            type_=sa.String(length=500),
+            existing_nullable=False,
+        )
\ No newline at end of file