In my case it was finaly a google block affecting gmail users:
"This message does not pass authentication checks (SPF and DKIM both 550-5.7.26 do not pass). SPF check for [gobmallorca.com] does not pass with ip: (xxxxxxxxxxx). To best protect our users from spam, the message has 550-5.7.26 been blocked".
Fixed with DNS modification in the server.