Redmine

After the upgrade to 4.0.5 receiving emails over imap stopped working.

rake redmine:email:receive_imap RAILS_ENV="production" host=mail.xxx.xx port=993 ssl=true username=xxx password=xxx

OpenSSL::SSL::SSLError: SSL_connect returned=1 errno=0 state=error: dh key too small
/usr/src/redmine/lib/redmine/imap.rb:30:in `new'
/usr/src/redmine/lib/redmine/imap.rb:30:in `check'
/usr/src/redmine/lib/tasks/email.rake:121:in `block (4 levels) in <top (required)>'
/usr/src/redmine/app/models/mailer.rb:612:in `with_synched_deliveries'
/usr/src/redmine/lib/tasks/email.rake:120:in `block (3 levels) in <top (required)>'
/usr/local/bundle/gems/rake-13.0.0/exe/rake:27:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
Tasks: TOP => redmine:email:receive_imap
(See full trace by running task with --trace)

on the mail server I see in the log:

TLS handshaking: SSL_accept() failed: error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure: SSL alert number 4

so it seemes to try to connect via sslv3 ?
but that is not enabled on the server.

I then tried to use starttls:

rake redmine:email:receive_imap RAILS_ENV="production" host=mail.xxx.xx port=143 starttls=true username=xxx password=xxx

but thats no working either:

OpenSSL::SSL::SSLError: SSL_write
/usr/src/redmine/lib/redmine/imap.rb:34:in `check'
/usr/src/redmine/lib/tasks/email.rake:121:in `block (4 levels) in <top (required)>'
/usr/src/redmine/app/models/mailer.rb:612:in `with_synched_deliveries'
/usr/src/redmine/lib/tasks/email.rake:120:in `block (3 levels) in <top (required)>'
/usr/local/bundle/gems/rake-13.0.0/exe/rake:27:in `<top (required)>'
/usr/local/bin/bundle:23:in `load'
/usr/local/bin/bundle:23:in `<main>'
Tasks: TOP => redmine:email:receive_imap
(See full trace by running task with --trace)

how can I fix the problem