Ronin supports custom SMTP so you can switch to your own SMTP servers under your Ronin account's settings page.
Custom SMTP Authentication
If you use Ronin's Custom SMTP feature, your outgoing invoice emails to customers will be sent using your SMTP relay with your SMTP credentials. In order to properly integrate, you'll need to look for the SMTP authentication details for your email provider.
For example, here are the SMTP authentication details for Gmail and Microsoft Office 365. Note that to use direct SMTP authentication on Google email services, you'll need to enable "Less Secure Apps" access
Google Specific Instructions
In the instance where you cannot authenticate your login for SMTP, you may need enable access after you've enabled "Less Secure Apps". You can turn "On" access by visiting this page in Google: https://myaccount.google.com/lesssecureapps. Additionally you may need to allow access by going to g.co/allowaccess.
If you want to send with a different From address than the username that you're using to authenticate into your Custom SMTP account, you'll need to make sure you have the sending emails added properly in Google Mail. By default, aliases can only receive, but cannot send.
You can add a sending alias by going to Settings -> Accounts -> Send mail as -> Add another email address you own -> And then adding the email alias.
See the following screenshot for a visual reference: