It seems that LinkedIn is refusing email from servers that don’t have a rDNS
This is the mail system at host mail.lucafrancesca.me.
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
mail-c.linkedin.com[2620:109:c006:104::215] said: 554 5.7.1 The sending
mail server at 2a01:4f8:100:242f::2 does not have a reverse
(address-to-name) DNS entry cf
http://en.wikipedia.org/wiki/Reverse_DNS_lookup (in reply to RCPT TO
Nice to see email being taken seriously.