Ahh, that makes sense … although I avoid M$ like the plague, so had no idea. Thanks for teaching me something new.
I am not familiar with lftp, and a quick Google search shows that it may be a good choice. However, I recommend using rsync. Again, you may be using a good alternative as it does look as though lftp synchronizes rather than just copies. I chose rsync because it only updates the changes, so there is typically much less data transfer involved.
As for why the hostname is ‘not resolved’ … I am honestly not certain. Quite often, people make simple unobvious mistakes with DNS, which from the info you PM’d me is not the case here. For me, MiaB would NOT use an alternate port with rsync, so I decided to pull the backups rather than push them - this was months ago before a solution was found that works.
Have you tried just testing backups via rsync with the IP address? Just to confirm that backups are working properly in the first place … this obviously would not work going forward but it would certainly help eliminate potential other issues.