Exchange 2003 mailbox backup

Hi, my master server is NBU 7.5.0.4 on RedHat 5. We are backing up MS Exchange 2003 individual mailboxes for some VIP accounts.

Previously for these VIPs, their AD accounts are the same as their email accounts, e.g. the AD account is abc and the email account is abc@company.com. However, recently some AD accounts are renamed but the email accounts remain the same, e.g. the AD account is abc and the email account becomes def@company.com. The backups of these emails failed.

My question is:

Should the AD account and the email account be the same in order for NBU to back up the individual mailbox? Can they be different? Thanks in advance.