How to debug pop3 emails not received


how can we debug the incoming emails of sales and support? Accoding to telnet tests the pop3 settings are ok, and Sync support mails is activated for support settings and Extract emails is activated for sales email.

No errors in Scheduler Log List.

ERPNext: v4.25.5
Frappe Framework: v4.14.1
Shopping Cart: v0.7.0

We were upgrading to v5:

bench switch-to-develop --upgrade
bench update

And everything seems to work fine except the email, we receive now this in Scheduler log:

Method: all, Handler:
Traceback (innermost last):
  File "/home/erpnext/frappe-bench/apps/frappe/frappe/", line 77, in scheduler_task
  File "/home/erpnext/frappe-bench/apps/erpnext/erpnext/support/doctype/support_ticket/", line 59, in get_support_mails
  File "/home/erpnext/frappe-bench/apps/frappe/frappe/utils/email_lib/", line 125, in __init__
  File "/home/erpnext/frappe-bench/apps/frappe/frappe/utils/email_lib/", line 153, in get_messages
  File "/home/erpnext/frappe-bench/apps/frappe/frappe/utils/email_lib/", line 141, in connect
    self.pop = Timed_POP3_SSL(, timeout=frappe.conf.get("pop_timeout"))
  File "/home/erpnext/frappe-bench/apps/frappe/frappe/utils/email_lib/", line 248, in __init__
    self._super.__init__(self, *args, **kwargs)
  File "/usr/lib64/python2.7/", line 350, in __init__
    raise socket.error, msg
 error: [Errno 101] Network is unreachable

Network issues?