TeamSideline does not offer post office/mailboxes for custom domains. Here are some alternatives that we recommend.

1. GSuite for Non-Profits (free) - https://www.google.com/nonprofits/offerings/apps-for-nonprofits/#!/. Go ahead and signup - it takes 2 to 14 business days for verification of your organization's non-profit status.

Here is a help article on how to get started: How to set up Google Workspace for Nonprofits

2. ZoHo - https://www.zoho.com/mail/ (https://www.zoho.com/mail/) .
** They have ad-free business mail and are reasonably priced.
** Mail Lite is $1/User/Month.
** 5 or less users and its free.

3. Office365 is a good option if you also use Outlook - https://products.office.com/en-us/compare-all-microsoft-office-products-4-column?&activetab=tab:primaryr2. They also have a free solution for non-profits - https://www.microsoft.com/en-us/nonprofits/microsoft-365?ef_id=8961f05df6c7135f396990816b3f005d:G:s&OCID=AID_SEM_8961f05df6c7135f396990816b3f005d:G:s&msclkid=8961f05df6c7135f396990816b3f005d.

If you decide and signup, you will provide support@teamsideline.com with the needed updates to your DNS and we'll get that completed for you. We are happy to work with you through this process.