I upgraded my Rails app to Rails 3.2.0 from 3.1.3 and found that my SMTP outgoing mail was no longer able to authenticate with my mail server.
Further investigation revealed that my ActionMailer config was using the configuration option :tls => true, which is now effectively :enable_starttls_auto => true. But of course. After that quick change it worked.
The specific error message I was seeing was:
SSL_connect returned=1 errno=0 state=SSLv2/v3 read server hello A: unknown protocol
Hope this helps somebody.