With email delegation in Google Apps for Business, is it possible to use an external email client like Outlook, Mac Mail etc. to access the emails?
I.e. an assistant using Mac Mail would be able to access the boss’s emails?
Since Gmail delegation is thought for Google Apps it makes sense to use it with Google Apps' Gmail.
Once the delegate is signed into their own own Gmail account, they can then access the other person's account from the account selection menu at the top of Gmail.
Also the mentioned restrictions on the delegations prohibits setting up an email client:
You won't be able to give anyone permission to change your account password or account settings, or chat on your behalf.
But an alternative to using just any client might be possible using the Google Apps Sync for Microsoft Outlook®: