We spoke to the ISP but didnt get a satisfactory answer, as we have migrated recently to outlook.com and we really want to stick around but this problem has been a dampner and its not justified to go back to using a mail client to access windows mails 

we changed the DNS to global settings but the ISP has said it might recur and will be left without a backup plan

the domain is brandcare.net 

we have about 35 users on the account and in a day our combined mailing might be in the range of 500 mails 

kindly advise, we have a emailer platform which we use on a another subdomain which we run campaigns for clients will that be a issue 

I would really appreciate if some one helps me out in this issue