Invalid Mail Server. Please rectify and try again

Traceback (most recent call last):
File “/home/frappe/frappe-bench/apps/frappe/frappe/desk/form/save.py”, line 22, in savedocs
doc.save()
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 256, in save
return self._save(*args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 290, in _save
self.run_before_save_methods()
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 809, in run_before_save_methods
self.run_method(“validate”)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 702, in run_method
out = Document.hook(fn)(self, *args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 924, in composer
return composed(self, method, *args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 907, in runner
add_to_return_value(self, fn(self, *args, **kwargs))
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 696, in
fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/doctype/email_account/email_account.py”, line 66, in validate
self.get_incoming_server()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/doctype/email_account/email_account.py”, line 163, in get_incoming_server
email_server.connect()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 44, in connect
return self.connect_imap()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 52, in connect_imap
self.imap = Timed_IMAP4_SSL(self.settings.host, timeout=frappe.conf.get(“pop_timeout”))
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 550, in init
self._super.init(self, *args, **kwargs)
File “/usr/lib/python2.7/imaplib.py”, line 1165, in init
IMAP4.init(self, host, port)
File “/usr/lib/python2.7/imaplib.py”, line 172, in init
self.open(host, port)
File “/usr/lib/python2.7/imaplib.py”, line 1176, in open
self.sock = socket.create_connection((host, port))
File “/usr/lib/python2.7/socket.py”, line 553, in create_connection
for res in getaddrinfo(host, port, 0, SOCK_STREAM):
gaierror: [Errno -2] Name or service not known

Traceback (most recent call last):
File “/home/frappe/frappe-bench/apps/frappe/frappe/app.py”, line 57, in application
response = frappe.handler.handle()
File “/home/frappe/frappe-bench/apps/frappe/frappe/handler.py”, line 22, in handle
data = execute_cmd(cmd)
File “/home/frappe/frappe-bench/apps/frappe/frappe/handler.py”, line 53, in execute_cmd
return frappe.call(method, **frappe.form_dict)
File “/home/frappe/frappe-bench/apps/frappe/frappe/init.py”, line 923, in call
return fn(*args, **newargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/desk/form/save.py”, line 22, in savedocs
doc.save()
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 256, in save
return self._save(*args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 290, in _save
self.run_before_save_methods()
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 809, in run_before_save_methods
self.run_method(“validate”)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 702, in run_method
out = Document.hook(fn)(self, *args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 924, in composer
return composed(self, method, *args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 907, in runner
add_to_return_value(self, fn(self, *args, **kwargs))
File “/home/frappe/frappe-bench/apps/frappe/frappe/model/document.py”, line 696, in
fn = lambda self, *args, **kwargs: getattr(self, method)(*args, **kwargs)
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/doctype/email_account/email_account.py”, line 66, in validate
self.get_incoming_server()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/doctype/email_account/email_account.py”, line 163, in get_incoming_server
email_server.connect()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 44, in connect
return self.connect_imap()
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 52, in connect_imap
self.imap = Timed_IMAP4_SSL(self.settings.host, timeout=frappe.conf.get(“pop_timeout”))
File “/home/frappe/frappe-bench/apps/frappe/frappe/email/receive.py”, line 550, in init
self._super.init(self, *args, **kwargs)
File “/usr/lib/python2.7/imaplib.py”, line 1165, in init
IMAP4.init(self, host, port)
File “/usr/lib/python2.7/imaplib.py”, line 172, in init
self.open(host, port)
File “/usr/lib/python2.7/imaplib.py”, line 1176, in open
self.sock = socket.create_connection((host, port))
File “/usr/lib/python2.7/socket.py”, line 553, in create_connection
for res in getaddrinfo(host, port, 0, SOCK_STREAM):
gaierror: [Errno -2] Name or service not known

check your port whether open or not
and also check the server address is correct

@markgates,
please tell me in detail how to check my port is open or not ?

Check in your firewall.
Check mail service is allowing imap and app login