If in doubt about who to address, for instance if you're e-mailing a group e-mail which you've never had any correspondence with previously, then address no one. A simple hi is normally sufficient:
Hi
I'm enquiring about blah. Stuff and things.
Kind regards
Your Name
People are more than used to informality in e-mails and it looks weird if you attempt to do more. If you're worried about appearing overly informal then use the team's name:
Hi Recruiting Team
Stuff and things...
In the case of )[email protected]_ writing Dear Join would appear a little strange; if you're really wedded to the idea of talking to an entity you can address the company - the people sat behind the e-mail are representing the company after all:
Hi Example Ltd
Stuff and things...
In the latter two examples feel free to substitute Hi for Dear; using Dear in this situation sounds less strange to me, in UK, but I imagine it'd be overly formal elsewhere.
If you're received an e-mail from someone then respond to the person or entity that signed the e-mail - you're not going to be incorrect then.
tl;dr: If in doubt don't mention anyone.