Like WMO suggested there are things that need to be checked. It's also possible that someone who previously had the IP address your vacation home is now using, had an infected computer and the IP is listed on a block list, as well as possibly having used that IP to send out spam, again, something that would have it placed on a block list. What is the IP address? We can look up on mx toolbox or spamhaus and other lists to see if there is a problem. We can also look up the dns on the IP and see if it has all the proper records associated with it.
What is the IP address?
I was going to ask that, but thought privacy prevented it. Speaking of IP, I wonder if OP could change their IP address by changing the WAN MAC address on the router and rebooting the modem. I think that works on Cox but I wonder if it works on Optimum? Delisting a blacklisted IP address is better IMO, but changing your IP in hope for one that isn't blacklisted is still a option. Then again that would do nothing if ALL the IP address by the ISP have no PTR.
