diff --git a/conf/settings.py b/conf/settings.py
index 7f149138..96db6469 100644
--- a/conf/settings.py
+++ b/conf/settings.py
@@ -89,6 +89,7 @@
 INCOMING_EMAIL_HOSTNAME = env("INCOMING_EMAIL_HOSTNAME", default="")
 INCOMING_EMAIL_USER = env("INCOMING_EMAIL_USER", default="")
 INCOMING_EMAIL_POP3_PORT = env("INCOMING_EMAIL_POP3_PORT", default=None)
+INCOMING_EMAIL_CHECK_LIMIT = env.int("INCOMING_EMAIL_CHECK_LIMIT", default=100)
 
 HMRC_TO_DIT_EMAIL_PASSWORD = env("HMRC_TO_DIT_EMAIL_PASSWORD", default="")
 HMRC_TO_DIT_EMAIL_HOSTNAME = env("HMRC_TO_DIT_EMAIL_HOSTNAME", default="")
diff --git a/mail/libraries/mailbox_service.py b/mail/libraries/mailbox_service.py
index 08918460..2ce511f2 100644
--- a/mail/libraries/mailbox_service.py
+++ b/mail/libraries/mailbox_service.py
@@ -70,13 +70,17 @@ def get_message_iterator(pop3_connection: POP3_SSL, username: str) -> Iterator[T
     mails: list
     _, mails, _ = pop3_connection.list()
     mailbox_config, _ = MailboxConfig.objects.get_or_create(username=username)
+    incoming_email_check_limit = settings.INCOMING_EMAIL_CHECK_LIMIT
 
-    # Check only the last 500 emails
+    # Check only the emails specified in the setting
     # Since we don't delete emails from these mailboxes the total number can be very high over a perio
     # and increases the processing time.
     # The mails is a list of message number and size - message number is an increasing value so the
     # latest emails will always be at the end.
-    mail_message_ids = [get_message_id(pop3_connection, m.decode(settings.DEFAULT_ENCODING)) for m in mails[-500:]]
+    mail_message_ids = [
+        get_message_id(pop3_connection, m.decode(settings.DEFAULT_ENCODING))
+        for m in mails[-incoming_email_check_limit:]
+    ]
 
     # these are mailbox message ids we've seen before
     read_messages = get_read_messages(mailbox_config)