For those not familiar with the processing of absentee ballots, all ballots received have to first be sorted by precinct, which is how they are counted, just like the poll votes. Then each has to have the signature of the voter verified against a digitized facsimile maintained in a special computer file, and the voter credited so that no one can vote twice. (We are limited to eight stations that can be used for verification or "validation").
Next, the identifying outer-envelope has to be removed and set aside for storage. This is to protect the privacy of the voter and to maintain the envelopes, which serve as the "poll book" for the mail ballots.
The ballot is then removed from the inner or secrecy envelope and inspected for corrections that the voter has made and which need to be fixed before the mark-sense or optical-scan reader can correctly read the vote.
Finally, the ballots are rebatched by precinct, boxed, and sent to the tabulators for the tally. When 70,000 ballots are received at once, as they were on Election Day and almost as many the next day, this process is not instantaneous.