JIRA's Email handling is not very efficient when dealing with IMAP. We should fix. It appears that whenever you call the message.getContent() method on a IMAP message with string body (i.e. HTML or TEXT), JavaMail goes to the server and fetches it. JavaMail does not seem to cache the body. This means that code like:

if (message.getContent() instanceof Multipart)
{
	final Multipart multipart = (Multipart) message.getContent();
	final Collection changeItemBeans = handleMultipart(multipart, message, issue);
	if ((changeItemBeans != null) && !changeItemBeans.isEmpty())
	{
		attachmentChangeItems.addAll(changeItemBeans);
	}
}

actually calls the server twice for some non-Multipart parts. For my example, in my case we called the server 8 times to get the message body.