Retry to send email when server unexpectedly disconnect

Closes #12790
(grafted from fc0afccf55b95644352655d8c081713df77d1662)

--HG--
branch : 7.0

trytond/trytond/sendmail.py

@@ -45,6 +45,14 @@ def sendmail(from_addr, to_addrs, msg, server=None, strict=False):
             time.sleep(0.02 * (retry - count))
         try:
             senderrs = server.sendmail(from_addr, to_addrs, msg.as_string())
+        except smtplib.SMTPServerDisconnected:
+            if count:
+                server = get_smtp_server(strict=strict)
+                if server:
+                    continue
+            if strict:
+                raise
+            logger.error('fail to send email', exc_info=True)
         except smtplib.SMTPResponseException as e:
             if count and 400 <= e.smtp_code <= 499 and hasattr(server, 'uri'):
                 server.quit()