If you have tried to send a listing or bulk email to a very large amount of contacts and it has failed, it has most likely timed out.
The bulk select tool in the contact module is not intended to support a large number of contacts at one time.
When you have a listing or email that you want to bulk send to contacts, we recommend using the E-marketing module instead:
The E-marketing module was developed specifically to send bulk email campaigns.
Sending the email or listing via this method should allow you to email large quantities of contacts in one hit with no time-out errors.