Article ID: 122502, created on Jul 29, 2014, last review on Jun 9, 2016

  • Applies to:
  • Plesk 12.0 for Linux
  • Plesk 11.0 for Linux
  • Plesk 11.5 for Linux
  • Plesk 10.4 for Linux/Unix


Mail authentication fails with the following error in the /var/log/maillog:

Jul  6 20:02:51 linux courier-pop3d: LOGIN FAILED, user=user@domain.tld, ip=[::ffff:]
Jul  6 20:02:51 linux courier-pop3d: authentication error: Input/output error


This is normal courier-authdaemon behaviour when it not able to authenticate user due to invalid credentials.

The POP3/IMAP server says "Temporary problem, please try again later" when a bad password is entered.

authdaemond tries each of the configured authentication modules in turn, until either one accepts the login, or they have all rejected it (in which case the usual "Login failed" error is returned, and the user can try again).

However, if one of these modules is unable to run because some resource is not available, then it gives a temporary failure response and no further modules are tried.

The error is more clear in Plesk 12.5.

Search Words


courier-pop3d: authentication error: Input/output error

aea4cd7bfd353ad7a1341a257ad4724a 56797cefb1efc9130f7c48a7d1db0f0c a914db3fdc7a53ddcfd1b2db8f5a1b9c 29d1e90fd304f01e6420fbe60f66f838 0a53c5a9ca65a74d37ef5c5eaeb55d7f 01bc4c8cf5b7f01f815a7ada004154a2 2a5151f57629129e26ff206d171fbb5f e335d9adf7edffca6a8af8039031a4c7 e8756e9388aeca36710ac39e739b2b37 dd0611b6086474193d9bf78e2b293040

Email subscription for changes to this article
Save as PDF