Note to readers: RoundCube 0.7.1 uses the Iloha IMAP Library. RoundCube 0.7.2 does not, so this particular problem may already be fixed.

In the past I’ve had to enable PLAIN IMAP authentication because older versions of M$ Outlook didn’t support CRAM-MD5 authentication. This means that my IMAP server advertises CRAM-MD5 as well as PLAIN as possible authentication methods.

All my clients who wanted to login using PLAIN cannot login using CRAM-MD5 because their passwords have to be stored in a different format.

A problem occurs when you set RoundCube’s “imap_auth_type” to “check”, because it picks CRAM-MD5 over PLAIN every time. I don’t want this to happen because some of my clients cannot login using CRAM-MD5. Ideally RoundCube should be following RFC3501:

If an AUTHENTICATE command fails with a NO response, the client MAY try another authentication mechanism by issuing another AUTHENTICATE command. It MAY also attempt to authenticate by using the LOGIN command

…but RoundCube doesn’t. To temporarily fix the problem you should be able to set “imap_auth_type” to “plain” so that RoundCube always uses PLAIN to authenticate against the IMAP server. However, I found that this does not work in 0.7.1 because of the following problem:

RoundCube passes options to the iil_Connect function of the Iloha IMAP Library. The options object includes a property “auth_method”, meant to control the authentication method, but this is never used, because the iil_Connect method expects this property to be named “imap”.

Line 382 of /program/include/rcmail.php is where the options object is defined – I simply changed ‘auth_method’ to ‘imap’.