In earlier days of e-mail and internet genealogy Message Boards and Mailing Lists were very popular. While they may not be quite as popular now, they are still a great source of help and information.
Rootsweb (owned by Ancestry.com) still has its surname mailing lists, that you can still subscribe to. You would use a common (or difficult to research) surname from your family tree, subscribe to the list, and be connected to other people also researching that name. There are also archives from the mailing lists that are searchable.
Rootsweb has also combined their message boards with Ancestry's, which can be a good place to ask for specific help (boards are listed by location or topic). Rootsweb, and the message boards, are free, so that's a big plus as well. This may be easier to look through, since the posts weren't originally e-mails, they are archived and easy to search.