Gmail a Spam

I'm having problems because all mail that is placed in Gmail, gets spammed.
The rest of the accounts arrive well.
I need to sort this out because my client stays.
Thank you very much.

Dear giacopazzi,

We always recommend to set the mailer to SMTP in the Joomla Global Configuration under the Server tab. This will avoid many mail problems, including your contact message be marked as SPAM.
Go to Global Configuration and set these options below accordingly to your server. If you are unsure how to do it, please contact your web hosting provider and he will be able to give you this information:

Mailer: SMTP Server
SMTP Authentication:
SMTP Security:
SMTP Port:
SMTP Username:
SMTP Password:
SMTP Host:

If you are using a Reseller Plan. When creating new accounts, make sure to enable SPF and DKIM records under "Email Authentication". If you don't know if you have correct SPF and DKIM records, then please contact your web hosting provider to configure it for you.

PS: I took the liberty to change your username to giacopazzi, instead of your email address. This will avoid spambots from harvesting your email address.

Best regards,