BBC has caught up now with the McCormack email:
The inquiry is presented with an email from campaigner Tim McCormack to Paula Vennells - chief executive of the Post Office between 2012 and 2019 - about the bug in the Horizon system.
McCormack writes that it’s the last chance for Vennells to accept what he's been telling her – there is evidence of the bug in Horizon.
The money doesn’t exist, he says in the email, adding the error could be the reason for many of the Justice For Sub-postmasters Alliance (JFSA) cases.
McCormack asks her to travel to the branch in question and see for herself.
McCormack continues that he wants to “appeal to your sense of decency and compassion” and accept that many of the claimants in the JFSA saga are honest.
If she ignores the email she will be exposed and possibly be open to criminal charges, McCormack adds.
The inquiry sees emails in which the execs discuss how to respond to this.
Williams then emails a reply saying that McCormack is a "bluffer" who expects the board to march to his tune. Williams says they should respond with a “straight bat”.
Counsel to the inquiry asks Williams if by this time he was aware of the bugs.
Williams replies that he was.
He's asked what he meant by a straight bat - Williams says it means "appropriately."