Incompatibility in the Mail API between the factory produced and component accepted types

Some (4) MimeMessageFactories in the Mail module extend the

abstract class AbstractIteratorMimeMessageFactory extends AbstractMimeMessageFactory<Iterator<MimeMessage>>

As a result, their return type is Iterator<MimeMessage> which is incompatible with the type accepted by MailSender#sendAsynchronously(Iterable<? extends MimeMessage> messages...).

In order to be able to use the Iterator<MimeMessage> result of the factory, one must do one of the following:

• >= Java8: () -> messages
• < Java 8: Create a wrapper class that returns Iterable<? extends MimeMessage> which simply wraps and re-produces the iterator
• Same as above, but use instead org.apache.commons.collections4.iterators.IteratorIterable and do new IteratorIterable(messages); (suggested by tmortagne)

The API should be consistent and use one of the 2 options (iterator or iterable) and not force the client to work around it.