Evidence for peer-review

My friend told me that I just need thank you emails but I asked an attorney who said I need both thank you emails and invitation emails. Which one is it!?

to Norma:

just thank you emails

to Norma:

Hey, thank you e-mails would serve the purpose.

to Norma:

I'd submit both. I have a friend who got RFE and officer asked for invitation evidence. Submitting both would be foolproof.