Is the location of the mail server important?

If you are a busy email user, it is recommended that you have the mail server in the same country unless you are using a large provider like G Suite.

If the mail server is in another country, users of your mail may experience slowdowns when downloading / downloading large attachments and when sending / receiving many emails. Synchronization via IMAP can also be slow if you have a lot of emails on the server. Since you have 40 users, and about 20 of them are heavy users, you might want to consider a vendor with a server close to you.

However, if users send emails from time to time, for example 5 to 10 emails per user per day, the location of the server should not be of importance to you.