If including a query, add a filter to only include constituents with Send mail to this address checked:
Address > Preferred Address > Preferred Send Mail to This Address equals Yes

OR

If the constituents do not have any valid addresses, check the box Has no valid addresses on the Bio1/Org1 tab under This constituent.
This checkbox can be used as a filter in the Export on the General tab under Include these constituents.

OR

Use address processing in Export which considers the Send Mail to this Address checkbox:
Address > Address Processing > <fields for address>