It has nothing to do with SPF, DKIM and such gadget (though it may help).

Google wants your mail host to have consistent reverse-dns records (ptr).

Which means :

host [your ip address]

should gives such results :

Using domain server:
Name: 8.8.8.8
Address: 8.8.8.8#53
Aliases:

[your ip address].in-addr.arpa domain name pointer [your mailhost fqdn]

Google's mail servers are really quite a pain to mail to.
Also beware if your mailhost has ipv6 enable, the reverse dns record 
should be consistent for ipv6 too.

Le 13/02/2017 à 13:40, Marcel de Rooy a écrit :
 My server is available at something like myserver.libriotech.no.
 Should KohaAdminEmailAddress (which is used for From by default) be library@myserver.libriotech.no or just library@libriotech.no?
 Depends on your exact configuration. Both domains may go the same ip address.
 Also check your reverse dns.
 When I check via mxtoolbox.com I do not get a response on myserver.libriotech.no
 But I cannot smtp check libriotech.no either.

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