Why is my e-mail address extremely long or consists of "xxxxx" only?

If your e-mail address consists of "xxxxx" only, you didn't gain access to "all" for your e-mail address within the Facebook privacy settings. This applies to the recommended Facebook settings.

If your e-mail address looks similar to this

apps+160497417310220.1800497135.ca56xxxxxxxxxxxxxxxxxxxx@proxymail.facebook.com

Facebook provides an e-mail proxy server. E-mails will be sent to Facebook first and then forwarded to your e-mail account. This is the default and only way to use e-mail via Facebook Connect.