Google Apps SMTP Relay Errors on Shared Hosting

I’m self hosting v5.2.17-C56 on a shared hosting account (BlueHost) attempting to get emails set up properly. My most recent attempt is to route the emails through my company’s Google Apps smtp, which works for emails generated via button click, but not for reminders or recurring invoices. For the reminders / recurring invoices, I receive the ‘Expected response code 250 but got an empty response’ error documented in the self hosted troubleshooting docs (Free Source Available Invoicing, Expenses & Time-Tracking | Invoice Ninja).

My question is what value do I add to the SERVER_NAME= variable in the .env file? Is that looking for the subdomain of the installation, primary domain of the shared server, the ip address of my shared server, or my hosting username? I tried payments.mydomainname.com, but got the same error. And trying one is very time consuming, as I have to wait a whole 24 hour cycle for the emails to fire again. Any help would be much appreciated, thanks!

@david any suggestions?

I believe SERVER_NAME should be the domain name of your app. ie acme.com