"LOGIN failed" loop

[ghost]

Hi together,

we configured a logstash adapter with this imap plugin to fetch emails from one email account.
All over all this plugins works as expected. However it seems to have trouble handling network issues:

Sometimes our exchange server is not reachable, especially in the night. This is logged by the plugin with "Server unavailable". If this occurs multiple times, the plugin falls into a "LOGIN failed" message loop: It writes this message every second and doesn't stop that until we kill the process. After a service restart, it is working again.
Although it writes every second "LOGIN failed" it doesn't really try to authenticate against the imap server.

Logstash
Version: 2.3.4
OS: SUSE Linux Enterprise Server 11 (x86_64) / 3.0.101-0.47.71-default
Config:
input { imap { host => "imap.host" password => "secret" user => "IMAPUSER" folder => "FOLDER" fetch_count => 500 port => 993 secure => true delete => true check_interval => 30 type => "TYPE" } }

Sample Error:

{:timestamp=>"2016-10-01T06:44:44.356000+0000", :message=>"A plugin had an unrecoverable error. Will restart this plugin.\n Plugin: <LogStash::Inputs::IMAP host=>\"imap.host\", password=><password>, user=>\"IMAPUSER\", folder=>\"IMAPFOLDER\", fetch_count=> 500, port=>993, secure=>true, delete=>true, check_interval=>5, type=>\"ticgmp\", codec=><LogStash::Codecs::Plain charset=>\"UTF-8\">, verify_cert=>true, lowercase_headers=>true, content_type=>\"text/plain\">\n Error: Server Unavailable. 15", :level=>:error} {:timestamp=>"2016-10-01T06:45:48.768000+0000", :message=>"A plugin had an unrecoverable error. Will restart this plugin.\n Plugin: <LogStash::Inputs::IMAP host=>\"imap.host\", password=><password>, user=>\"IMAPUSER\", folder=>\"IMAPFOLDER\", fetch_count=>500, port=>993, secure=>true, delete=>true, check_interval=>5, type=>\"ticgmp\", codec=><LogStash::Codecs::Plain charset=>\"UTF-8\">, verify_cert=>true, lowercase_headers=>true, content_type=>\"text/plain\">\n Error: LOGIN failed.", :level=>:error} {:timestamp=>"2016-10-01T06:45:49.821000+0000", :message=>"A plugin had an unrecoverable error. Will restart this plugin.\n Plugin: <LogStash::Inputs::IMAP host=>\"imap.host\", password=><password>, user=>\"IMAPUSER\", folder=>\"IMAPFOLDER\", fetch_count=>500, port=>993, secure=>true, delete=>true, check_interval=>5, type=>\"ticgmp\", codec=><LogStash::Codecs::Plain charset=>\"UTF-8\">, verify_cert=>true, lowercase_headers=>true, content_type=>\"text/plain\">\n Error: LOGIN failed.", :level=>:error} {:timestamp=>"2016-10-01T06:45:50.869000+0000", :message=>"A plugin had an unrecoverable error. Will restart this plugin.\n Plugin: <LogStash::Inputs::IMAP host=>\"imap.host\", password=><password>, user=>\"IMAPUSER\", folder=>\"IMAPFOLDER\", fetch_count=>500, port=>993, secure=>true, delete=>true, check_interval=>5, type=>\"ticgmp\", codec=><LogStash::Codecs::Plain charset=>\"UTF-8\">, verify_cert=>true, lowercase_headers=>true, content_type=>\"text/plain\">\n Error: LOGIN failed.", :level=>:error} {:timestamp=>"2016-10-01T06:45:51.926000+0000", :message=>"A plugin had an unrecoverable error. Will restart this plugin.\n Plugin: <LogStash::Inputs::IMAP host=>\"imap.host\", password=><password>, user=>\"IMAPUSER\", folder=>\"IMAPFOLDER\", fetch_count=>500, port=>993, secure=>true, delete=>true, check_interval=>5, type=>\"ticgmp\", codec=><LogStash::Codecs::Plain charset=>\"UTF-8\">, verify_cert=>true, lowercase_headers=>true, content_type=>\"text/plain\">\n Error: LOGIN failed.", :level=>:error}

IMAP Server: MS Exchange 2013