Issue with resolving email address

We use Microsoft Dynamics CRM 2016, without the email client.

We have multiple help desks working with queues.

The issue is with the to-address of an e-mail.

Most of the mails we sent are to an account in CRM and the email address of that account is used.

In a few exceptional situations we sent an email to someone not in our database.

Then we enter the email address manually.

Now in our database we have a record with email address xxx.yyy.zzzzzz@gmail.com. So with dots in the part before '@'. 

The user enters an address on the mail: xxx_yyy_zzzzzz@gmail.com (so with underlines in the part before '@').

What happens then is that CRM resolves the user entered address to xxx.yyy.zzzzzz@gmail.com.

So the underscores '_' in the manual entered address are ignored and an email address with dots is selected. 

This can result in sending privacy sensitive information to the wrong email address.