No longer receiving notification & password restore mails.

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Hiya c5 community,

Apperantly the server my site was hosted on was faulty so my host moved my site to a new server. However ever since they did that, we can no longer receive mail from things like forms or even "Retrieve Password"

I did some googling around and people mention that I could try editing my site.php but I can't find that file (most of the threads I found were from 2010 - 2013)

Does anyone know how to fix this? Or should I contact my host?

Edit: I tested the mail via the Dashboard > mail > test and it says it's succesfully send (but it never arrived in my mailbox).