Pretend we have no idea who force9 or Greenby are and you will be getting close to where I am now. I am guessing that they are either an ISP or hosting provider, or at least one of them is. Google pointed me to this question and answer page https://greenby.com/faq so I know a little more, but seriously you are going to have to offer much more in the way of information is anyone is going to offer constructive assistance. My first reaction is when was your account migrated? My second was what is the error you receive? My third was have you a third party antivirus? As they are notorious for messing up email connections disabling them is often the first diagnostic task. ( on Windows defender kicks in as soon as the third party product gets out of the way so you are not left hanging out there with no protection. I did try looking at the plus net community for information but they have blocked anyone not in the UK accessing their website (or certainly from Australia, we must be a threat to their business somehow I guess). So their support site is only available to you not me. https://community.plus.net/t5/Email/Force9-migration-to-Greenby/td-p/2027804