Addresser

An addresser is defined as a person who addresses someone by direct spoken or written communication, or simply a person who gives an address or speech [Wiktionary.org].
Addresser is a term opposite to the addressee.
The distinction between addresser and addressee is that an addressee is a person to which something (i.e., a letter or message) is addressed, in contrast, an addresser is a person who provides an address or speech [Wikidiff].
A person who conveys a message to a specific audience is called an addresser. Every communication involves a sender and a receiver (or addresser and addressee). The addresser sets up the context of the message, to be understood. This includes the conditions and environment it’s given in, and where, how and when the message is given [Lucidchart].

Sources:

⠀ Addressee. Wikidiff. Retrieved from: https://wikidiff.com/addresser/addressee.

⠀ Jakobson’s functions of language. Lucidchart. Retrieved from: https://www.lucidchart.com/blog/jakobsons-functions-of-language.