SMTP / SOAP Authentication fails

[drei]

I've got some issues with authentication.
The situation at the moment:

• authentication for IMAP access is working
• authentication for POP access is working
• authentication for SMTP fails
• authentication for SOAP requests fails (e.g. CalDAV requests)

I mainly have a hard time figuring out where in the logs I could find some useful information. The only thing I was able to find in the logs comes from 'zimbra.log':

Jun 27 11:50:26 server.domain.com postfix/smtpd[608]: warning: client.host.name[xxx.xxx.xxx.xxx]: SASL PLAIN authentication failed: authentication failure

The same is logged if SMTP authentication is tried with SASL CRAM-MD5.

Configuration in regards of authentication options for the server in question are:

zimbraMtaAuthEnabled: TRUE
zimbraMtaAuthHost: server.domain.com
zimbraMtaAuthTarget: TRUE
zimbraMtaAuthURL: https://server.domain.com/service/soap/
zimbraMtaTlsAuthOnly: FALSE
zimbraMailMode: mixed

What would be a next step to debug this situation?
Thank in advance for any hints.

[phoenix]

SMTP Auth Problems - Zimbra :: Wiki

[drei]

Thanks for the link, phoenix.
I wouldn't have posted here though if I hadn't read and followed that wiki article already.

I'd like to set things up that SMTP with authentication is possible as well as implicit authorization by first polling the mailbox by IMAP or POP.

[drei]

I still wasn't able to resolve this issue regarding the SMTP authentication, SOAP authentication is working.
Mainly because I failed so far to figure out at what logs to look to find some hints about where the problem may be…

Is there anybody willing to share some information about how I can possibly debug this issue?

Thanks.