The limitation can be seen on the official documentation for if statements in hubl.
I see that “Courtney Fantinato” from this slack thread seems to need if-statements for emails, too. @ridingforlife seems to have a quite similar problem that is mentioned in this thread.
There could be more problems with the combination of emails and contact properties, but I don’t know much about these. I have also seen that Hubspot seems to have problem with
{% set %}
and contact properties, but I did not dig into it yet.
The if statement seemed more crucial to me, so I only focused on that problem in this idea.