SPF and DKIM not working on VestaCP cloud server

All the emails sent by the accounts of my server are being received into the Spam folder of gmail receivers. I've got DKIM support checked in my mail domain configuration in Vesta and I also checked in the dns registries both SPF and DKIM entries are OK:

v=spf1 a mx ip4:xxx.xxx.xxx.xxx ~all v=DKIM1; k=rsa; p=balblablablabla..

I sent a test mail to www.mail-tester.com and the results say that my DKIM signature is not valid: - [SPF] domain.com doesn't allow my server xxx.xxx.xxx.xxx to use admin@domain.com - We could'nt get your public key. Please check if you added the entry DN TXT DKIM in your domain domain.com using the selector mail.

Any clue on how to solve this?