How would a mortgage offer be confirmed by the lender?

Hi,

Sorry for the ambiguous title....

I gave a call to my mortgage adviser yesterday and he confirmed he will offer the mortgage before 5pm.

Till now, I didnt receive any email or phone call from him and I am a bit worried (we have a really tight deadline for the entry date and other stuff to be prepared before that).

I am just wondering, how would the lender confirm that they will make the formal mortgage offer to us? Is it by email or by post?

Thank you.
D