We some times get the following failure on Github CI:
```
expected StandardError with message matching /some.host/, got #<Socket::ResolutionError: getaddrinfo: Temporary failure in name resolution> with backtrace:
```
Why this change?
This is a follow up to 897be75941.
When updating `net-smtp` from `0.4.x` to `0.5.x`, our test suite passed
but the error `ArgumentError: SMTP-AUTH requested but missing user name`
was being thrown in production leading to emails being failed to send
out via SMTP.
This commit adds a test to ensure that our production SMTP settings will
at least attemp to connect to an SMTP server.
Alan Guo Xiang Tan