smtplib: catch OSError, not SMTPException

Some, but not all, types of connection error are caught by smtplib and
reraised as an smtplib.SMTPException. Notably, TimeoutError,
socket.gaierror (name resolution failure), and ConnectionRefusedError
and are not caught.

The more generic OSError should be caught here instead.

Resolves #1905

dnf/automatic/emitter.py

@@ -106,7 +106,7 @@ def commit(self):
             smtp = smtplib.SMTP(self._conf.email_host, timeout=300)
             smtp.sendmail(email_from, email_to, message.as_string())
             smtp.close()
-        except smtplib.SMTPException as exc:
+        except OSError as exc:
             msg = _("Failed to send an email via '%s': %s") % (
                 self._conf.email_host, exc)
             logger.error(msg)