Hello,
I recently installed an OS7400 with an OS7200 expansion cabinet. When calling in to the site through the auto attendent from an outside line, and accessing an extension, no-answer calls forward to voicemail as they should. When calling the same extension from another internal extension, the call just rings and rings, and doesn't forward to voicemail. This is only happening with certain extensions. Anybody have any ideas?

Your external no answer forward is probably the result of transfer recall. Calling internally you need to look at mmc102 to forward calls or mmc 316 preset fna

Like PVJ said, check 316 and set it to 5049 for both. That should send the calls to Voicemail after the allotted timer expires