Make E-Mail sent to address not go into spam

I have a problem I can't seem to solve. There are many e-mails sent to some address which are being sent to the junk e-mail folder.

I *have* added that address in the "safe recipients" list, but it's still sending some of it to the junk folder.

Those mails are being generated by PHP (it's a contact form), and they are sent with the "from" address of the customer, but the recipient's address is always the same (that's the one I've added to the safe recipients list).

Just  to make sure, this is where I'm adding the "to" address (it's in Spanish but should be easily understood... the icon is unique to that tab):

And this is an e-mail which went to the junk folder:

As I understand it, anything sent to that address: soporte@la(xxxxxxxxxx.x)sshould never go into junk... or am I understanding it differently?

Also, is there any way I can make a rule so that I can prevent it going into the junk folder with other rules (like subject or something)?

Thanks

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