Your event sponsors are not involved out of the goodness of their hearts. They want something back—probably publicity or awareness-raising. Sponsor co-marketing is therefore an important part of event marketing.
When you first approach sponsors, you will need to lay out a clear package of sponsor benefits. This may include, for example, their logo on event communications and signage, details of the company and what it offers included in the press pack, and shared publicity. There is more about this here. However, you may also want to agree further marketing opportunities.
The previous email made clear that journalists need stories. It can be helpful if one of your sponsors is planning to make an announcement of some sort at the event, and is prepared to have it trailed ahead of time. This can be mutually beneficial, ensuring that journalists attend the event, and the announcement is fully reported.