"Freemail" is a term for any email service that provides email accounts free of charge, such as Gmail, Yahoo, Hotmail, etc. While these are a cost-effective way to provide an email account to your employees, they can create issues with email deliverability.
SingleOps uses the user's email as the "Reply-to" for emails sent out of SingleOps. This allows the customer to converse directly with the person who sent them their proposal, invoice, etc. However, many spam filters flag emails that use Freemail domains in the "reply-to" address. So, to ensure deliverability, we suggest that if you have a user that uses a freemail domain and will be sending emails in SingleOps that you check the "Use Account Email as Reply To" option.