Syslogappender sends stacktrace lines separately to syslog.
Currently the suffixPattern is not applied to these stackTrace lines, and the user has no way of controlling the format of these lines.

I Implemented an optional stacktraceSuffixPattern parameter to SyslogAppender that allows the user to control the format of stacktrace lines too. If this parameter is not set, it defaults to the default formatting, which is the old hardcoded formatting (i.e. TAB <the stacktrace line>).

https://github.com/qos-ch/logback/pull/46