diff --git a/job_runner.py b/job_runner.py
index 6674964a..90b018ab 100644
--- a/job_runner.py
+++ b/job_runner.py
@@ -198,13 +198,18 @@ def process_job(job: Job):
             onboarding_mailbox(user)
     elif job.name == config.JOB_ONBOARDING_4:
         user_id = job.payload.get("user_id")
-        user = User.get(user_id)
+        user: User = User.get(user_id)
 
         # user might delete their account in the meantime
         # or disable the notification
         if user and user.notification and user.activated:
-            LOG.d("send onboarding pgp email to user %s", user)
-            onboarding_pgp(user)
+            # if user only has 1 mailbox which is Proton then do not send PGP onboarding email
+            mailboxes = user.mailboxes()
+            if len(mailboxes) == 1 and mailboxes[0].is_proton():
+                LOG.d("Do not send onboarding PGP email to Proton mailbox")
+            else:
+                LOG.d("send onboarding pgp email to user %s", user)
+                onboarding_pgp(user)
 
     elif job.name == config.JOB_BATCH_IMPORT:
         batch_import_id = job.payload.get("batch_import_id")