Step 1: Go through the sample email-to-case process as explained in blog: How to design a support process (email based) when using Dynamics 365 for Customer Service?
Step 2: Set up Mailbox (can be shared mailbox too) e.g. firstname.lastname@example.org
Step 3: Set up the Queue (e.g. Zap Support Queue having incoming email address as “email@example.com”. This ensures that the emails sent to “firstname.lastname@example.org” are received in this Queue.
Refer KB article (for Steps 1 and 2): link
Step 4: Install Zap Helpdesk Solution. Request email@example.com for latest zap helpdesk app solution file.
Step 5: Register the license. This will automatically start your 15-day trial. Refer KB article: link
Step 6: Provide Security roles: Refer KB article: link
Step 7: Configure Helpdesk settings (Create Zap_HD_Configuration record for each queue that needs to create Case automatically). Refer KB article: link
Step 8: Configure QuickEmailReplyUser Settings link
Step 9: Configure Canned Responses and Categories link