Ik don't think so...
Try a 'nslookup -query=AAAA server2.whitelabel-reseller.nl' to make sure you have an AAAA record for server2.whitelabel-reseller.nl and check if you have rdns on that ipv6 record.
Or disable ipv6 and sent using ipv4.
From over here it doesn't look like you have a AAAA record with your ipv6 server address and you don't have the rdns for ipv6 set correctly.
You are correct the records didnt exist i added now, or isp doesnt deliver reverse dns for ipv6 yet so cant change that part.
Issue is still there gona try adding interface= with the ipv4 ip