diff --git a/tox.ini b/tox.ini
index 15353917ac2..6a54b437098 100644
--- a/tox.ini
+++ b/tox.ini
@@ -380,6 +380,7 @@ deps =
     nbmake
     db-dtypes
     google-cloud-bigquery
+    aiosmtpd
 changedir = {toxinidir}/notebooks
 allowlist_externals =
     bash
@@ -494,6 +495,7 @@ deps =
     nbmake
     db-dtypes
     google-cloud-bigquery
+    aiosmtpd
 changedir = {toxinidir}/notebooks
 allowlist_externals =
     bash