Hi, I am getting a similar error. Like Dominik, I am not able to see the Enable SASL Authentication check box
I am on Jenkins 1.651.3 Jabber plugin v 1.35, instant messaging plugin 1.35

Here is the message I am getting.

Jun 29, 2016 11:19:22 PM INFO hudson.plugins.im.IMConnectionProvider$ConnectorRunnable run
Reconnect failed. Next connection attempt in 2 minutes
Jun 29, 2016 11:21:22 PM INFO hudson.plugins.jabber.im.transport.JabberIMConnection createConnection
Trying to connect to XMPP on /efi.com
Jun 29, 2016 11:21:23 PM WARNING hudson.plugins.jabber.im.transport.JabberIMConnection connect
org.jivesoftware.smack.sasl.SASLErrorException: SASLError using PLAIN: not-authorized
at org.jivesoftware.smack.SASLAuthentication.authenticate(SASLAuthentication.java:348)
at org.jivesoftware.smack.tcp.XMPPTCPConnection.login(XMPPTCPConnection.java:244)
at hudson.plugins.jabber.im.transport.JabberIMConnection.createConnection(JabberIMConnection.java:430)
at hudson.plugins.jabber.im.transport.JabberIMConnection.connect(JabberIMConnection.java:189)
at hudson.plugins.jabber.im.transport.JabberIMConnectionProvider.createConnection(JabberIMConnectionProvider.java:42)
at hudson.plugins.im.IMConnectionProvider.create(IMConnectionProvider.java:59)
at hudson.plugins.im.IMConnectionProvider.access$500(IMConnectionProvider.java:16)
at hudson.plugins.im.IMConnectionProvider$ConnectorRunnable.run(IMConnectionProvider.java:165)
at java.lang.Thread.run(Unknown Source)

Got the same problem here. Is it a jenkins version option? My Jenkins version here is 1.651.3

Same problem here:

Oct 13, 2016 12:33:26 PM org.jivesoftware.smack.sasl.SASLError fromString
WARNING: Could not transform string 'text' to SASLError
java.lang.IllegalArgumentException: No enum constant org.jivesoftware.smack.sasl.SASLError.text
        at java.lang.Enum.valueOf(Enum.java:238)
        at org.jivesoftware.smack.sasl.SASLError.valueOf(SASLError.java:22)
        at org.jivesoftware.smack.sasl.SASLError.fromString(SASLError.java:46)
        at org.jivesoftware.smack.sasl.SASLMechanism$SASLFailure.<init>(SASLMechanism.java:357)
        at org.jivesoftware.smack.util.PacketParserUtils.parseSASLFailure(PacketParserUtils.java:720)
        at org.jivesoftware.smack.tcp.PacketReader.parsePackets(PacketReader.java:253)
        at org.jivesoftware.smack.tcp.PacketReader.access$000(PacketReader.java:47)
        at org.jivesoftware.smack.tcp.PacketReader$1.run(PacketReader.java:81)

Oct 13, 2016 12:33:26 PM hudson.plugins.jabber.im.transport.JabberIMConnection connect
WARNING: org.jivesoftware.smack.sasl.SASLErrorException: SASLError using PLAIN: text
        at org.jivesoftware.smack.SASLAuthentication.authenticate(SASLAuthentication.java:348)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection.login(XMPPTCPConnection.java:244)
        at hudson.plugins.jabber.im.transport.JabberIMConnection.createConnection(JabberIMConnection.java:430)
        at hudson.plugins.jabber.im.transport.JabberIMConnection.connect(JabberIMConnection.java:189)
        at hudson.plugins.jabber.im.transport.JabberIMConnectionProvider.createConnection(JabberIMConnectionProvider.java:42)
        at hudson.plugins.im.IMConnectionProvider.create(IMConnectionProvider.java:59)
        at hudson.plugins.im.IMConnectionProvider.access$500(IMConnectionProvider.java:16)
        at hudson.plugins.im.IMConnectionProvider$ConnectorRunnable.run(IMConnectionProvider.java:165)
        at java.lang.Thread.run(Thread.java:745)

Jenkins: 2.7.1
instant-messaging-plugin: 1.35
jabber notifier plugin: 1.35

I cant find a checkbox for activation of SASL too..

Any update on this? 2 more have reported in the last 2 months. and I am waiting since June. I see the same results in Jenkins ver. 2.19.2

This is really a blocker for us. We cant switch our Openfire Server to SSO because then Jenkins would be locked-out.
There should be an option where you can choose to use GSSAPI or PLAIN

Any update on this?

SASL is exclusively used by the jabber-plugin. There is no option any more because it's always used.

If you see

" org.jivesoftware.smack.sasl.SASLErrorException: SASLError using PLAIN: not-authorized"

then this means that Smack tried to perform SASL authentication using the PLAIN mechanism and received a 'not-autahorized' reply from the server. Which usually means that your username and/or password is wrong.

The problem reported by Sebastian at https://issues.jenkins-ci.org/browse/JENKINS-31979?focusedCommentId=273422&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-273422 is actually different. It is possibly fixed once Smack is updated to 4.1.9 (JENKINS-45599). The code is already in master, you could clone it, build the plugin (mvn package) and see if it fixes the issue for you.