[Dovecot] How LDA deliver mail

hi,all

I read some part of the source code for studying and interesting. But i face trouble when I read the 'deliver.c'.
In file 'deliver.c' on line 812 , there is a function named 'deliver_mail', see below:
deliver_mail(storage, mail, destination, mailbox)

I couldn't find out where is this function defined and how it was linked.

Thank u for your help.