NO, you can't test this without sniffing traffic or reviewing logs on the receiving server.
The receiving email system will allow encrypted or unencrypted mail. It's up to the sending email system to require TLS or drop. For google apps (aka gsuite aka google work), this is configurable for specific domains.
There are a couple email flows here.
1. Client -&...
You can determine whether or not an SMTP server enforces STARTTLS using telnet.
Here is an example using smtp.gmail.com, which does enforce STARTTLS.
First, open a connection to smtp.gmail.com on port 587 using telnet:
telnet smtp.gmail.com 587
smtp.gmail.com responds with:
Escape character is '^]'.
220 smtp.gmail.com ESMTP 6sm4582570qkv.115 - gsmtp