What exceptions can be raised by action mailer

We've found this list works pretty well for standard errors that you might want to retry on:

[ EOFError,
IOError,
TimeoutError,
Errno::ECONNRESET,
Errno::ECONNABORTED,
Errno::EPIPE,
Errno::ETIMEDOUT,
Net::SMTPAuthenticationError,
Net::SMTPServerBusy,
Net::SMTPSyntaxError,
Net::SMTPUnknownError,
OpenSSL::SSL::SSLError
]

Note that I didn't include Net::SMTPFatalError because it is often a permanent failure (like a blacklisted email address).