Mail authentication fails: authentication error: Input/output error

Refers to:

  • Plesk 12.5 for Linux
  • Plesk 10.4 for Linux
  • Plesk 11.0 for Linux
  • Plesk 11.5 for Linux
  • Plesk 12.0 for Linux

Created:

2016-11-16 12:51:59 UTC

Modified:

2017-01-28 02:43:07 UTC

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Mail authentication fails: authentication error: Input/output error

Symptoms

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:192.168.133.219]
Jul 6 20:02:51 linux courier-pop3d: authentication error: Input/output error

Resolution

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.

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