There are several key issues that you will face regardless of which vendors you choose for your new messaging and collaboration infrastructure.  Rely on the experience of Technotics to help you master these issues in your domain from your first period of coexistence to the complete implementation of your new mail environment. 

Network Considerations

Your network infrastructure and the bandwidth you provide in most cases are currently adequate. But will it be enough to support the demands of an Internet based messaging solution?

Mail Routing Infrastructure

The process of moving between email systems will not happen overnight. There will be a transition period during which both systems will be required to interact as transparently a possible. This means that all current subdomain messaging infrastructures must be respected by both entities. Messages to and from users in the same domain, along with replies, multiple levels of replies to replies must be free from routing issues, and this can only be possible through well engineered, synchronized directory structures on the old and new systems.

Meetings, calendaring and resource reservations

All enterprises schedule meetings well into the future. You need methodologies to migrate these collaboration objects from your old system to the new one, hopefully without requiring a manual re-entering of the data. An auto-synchronization of the meeting data between the two systems would be ideal.

Security and Single sign on

Since most of the available choices rely on the integration of HTTP based resources with your existing infrastructure, a simplified security methodology for user access is extremely important. Synchronization of passwords between systems also becomes critical.  A vital part of your implementation should be focused around using a federated security methodology that incorporates your existing security infrastructure into the new system.  There are many choices in this arena.

Migration of existing email

Migration of existing mail to the new system is a major decision, as there can be substatntial additional costs associated with the retention of old mail. You must carefully examine each vendors options in this area to sensibly set requirements as to how much pre-existing email will be retained. In some cases, it is more cost effective to retain some elements of the existing system for users access while gradually transitioning to the new system. But there are many other options to consider here as well.

User provisioning

Be sure to carefully examine the user provisioning methods provided by the new mail service. There are significant variations from vendor to vendor. In some cases, on-premises servers are still required for user management even thought the messaging services themselves are provided exclusively in the cloud.