I know this post is old but I just had the same problem and didn't get a clear answer.

If you have 2 accounts one pop and one the exchange but the pop does not want to send if your offline.

The following method solved my problem.

1. Open your EMC
2. Select Recipient Configuration
3. Select your users -> Properties
4. Select TAB -> E-mail Addresses
5. Uncheck the check box Automatically update e-mail addresses based on e-mail address policy

This is not the correct method to receive and send your mail at home without being connected to the office network but a quick and easy method.