Hi, I upgraded logback to 1.2.9 (from 1.2.3) in my webapp (running under tomcat) and now my SMTPAppender configuration is not working. I have file appenders configured too, but they are all working. Relevant config from logback.xml : <property name="SERVER_NAME" value="XXX" /> <property name="CONTEXT_PATH" value="XXX" /> <property name="LOG_DIR" value="${catalina.base}/logs/${CONTEXT_PATH}" scope="system" /> <appender name="email" class="ch.qos.logback.classic.net.SMTPAppender"> <sessionViaJNDI>true</sessionViaJNDI> <jndiLocation>java:comp/env/mail/XXX</jndiLocation> <to>XXX</to> <from>XXX</from> <subject>XXX</subject> <layout class="ch.qos.logback.classic.PatternLayout"> <pattern>%date{HH:mm:ss.SSS} [%thread] [%level] %logger#%line %n%n%mdc%n%message%n</pattern> </layout> <cyclicBufferTracker class="ch.qos.logback.core.spi.CyclicBufferTracker"> <bufferSize>1</bufferSize> </cyclicBufferTracker> <includeCallerData>true</includeCallerData> </appender> Relevant resource definition in context.xml <Resource name="mail/XXX" auth="Container" type="javax.mail.Session" mail.transport.protocol="smtps" mail.smtp.starttls.enable="true" mail.smtp.host="XXX" mail.smtp.port="587" /> Found in tomcat's default log: 23:51:33,656 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - About to instantiate appender of type [ch.qos.logback.classic.net.SMTPAppender] 23:51:33,669 |-INFO in ch.qos.logback.core.joran.action.AppenderAction - Naming appender as [email] 23:51:33,711 |-INFO in ch.qos.logback.classic.net.SMTPAppender[email] - Looking up javax.mail.Session at JNDI location [java:comp/env/mail/XXX] 23:51:33,720 |-ERROR in ch.qos.logback.classic.net.SMTPAppender[email] - Failed to obtain javax.mail.Session from JNDI location [java:comp/env/mail/XXX] 23:51:33,720 |-ERROR in ch.qos.logback.classic.net.SMTPAppender[email] - Failed to obtain javax.mail.Session. Cannot start. Nothing else was changed, I just uploaded the new jars and restarted tomcat and now it fails. Downgraded to 1.2.7 and SMTPAppender works again.