I'm a kind of a novice in web development along with a new user to SO. Here's what I wish to implement for any client. They will use gmail custom-email application his or her corporate email. They would like to restrict use of the website private area for customers by having an email account using their company (that is really a gmail account). Something similar to what we should have for login into SO. Only SO allows any gmail/yahoo etc user to login however they want only ppl using their custom gmail email id. Any help or suggestions could be great..

And So I would most likely rock it to ensure that registration requires an @yourcompanydomain email. Ignore the gmail factor, and concentrate more about the syntax from the current email address being registered. Then, require email verification.

I went an identical script for the worker perks portal, simply checked on registration for @mycompanydomain within the email. Whether it did not exist, they cannot proceed.

This really is typically implemented with OpenID.

Based on your bank account configuration, you might use IMAP or POP3, but OpenID is going to be much more flexible, because it will not rely on specific configurations for every user account.