MAS 90 Reseller | MAS90 Reseller MTSI is a team of Certified Sage MAS Consultants and Microsoft Certified Systems Engineers To be renowned Sage MAS 90 Reseller means one has to be someone in authority with regards to the product. MTSI is a team of dedicated Certified Sage MAS Consultants who are at the same time Microsoft Certified Systems Engineers (MCSE). Having these titles and credibility means that we are experts in the Sage MAS 90 software and we can fully troubleshoot problems related to computer hardware and networking as well.