This is the mail system at host smtp2.osuosl.org.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
dsanchevel2@educacion.navarra.es: host aspmx.l.google.com[2607:f8b0:4001:c1d::1b] said: 550-5.7.1 The user or domain that you are sending to (or from) has a policy that 550-5.7.1 prohibited the mail that you sent. Please contact your domain 550-5.7.1 administrator for further details. For more information, go to 550 5.7.1 https://support.google.com/a/answer/172179 e9e14a558f8ab-3a344de9a3fsi43902215ab.99 - gsmtp (in reply to end of DATA command)