Is there a right way to answer emails that signed as:

...Thank you,
John Doe and Jenna Doe


Do I start with Hi John and Jenna or just pick one name??

If they signed it from both of them, that is how I would address it. Ignoring one is about the same as ignoring one of them in a face-to-face meeting.

~ Linda

I would write it in this way...

"Hi Jenna and John"

In Germany (perhaps in entire Europe) the name of the woman always comes first.

Or just "Hi:"

Thanks!
I usually reply with both names. I try to guess who wrote the email and put his/her name first. Otherwise I see how they signed it and put it in that order.

Same as above..Hi John and Jenna,

Thank you for contacting us for additional information...yada yada yada...At least that is the way I do it..Doesn't make it right, but it works for me...Yvette

Both names.

Both names, in the order they listed it, at least that's how it is in the U.S. Most of the time I see the woman's name first.