You need to look at program 24-09, sounds like it's not set for some or all extensions. The reason AA transferred your call to the user's mailbox on no answer is because of transfer recall, (AA being the extension transferring the call.)

There is no reason for anyone to wait for ring back to complete transferring calls. If there is a DSS key, while on the call press the DSS key and hang up. If no DSS key press the transfer key, dial extension, hang up. To transfer directly to the user voicemail, follow the same procedure but press 8 on the keypad afterwards and hang up, (8 has the letter V for voicemail)

We get old too soon, smart too late