Email server setup

Hello,

We are a startup company (IT based).

At present, we are planning for an Email Based Data Transfer method for exchanging critical documents with our international partners.

In order to achieve this and also ensuring a rather secure data exchange, do we need to setup an inhouse email server? If yes, then what are the best choices for email servers, keeping in mind that we are a small company.

We have a domain name say, @company.com

We truly appreciate your valuable input.
Regards.