Quick tips for planning and testing Exchange to Microsoft 365 Migration

Migration from Exchange to Microsoft 365 brings some cool new modern features but it has to be planned before starting it. After planning, testing helps us to identify how the mail flow works so that in case of any issues, it is much easy to troubleshoot.

Problem: Migration to be done with minimum downtime. No emails should bounce because of any misconfiguration. Configuring outlook on users computers to connect to Microsoft 365 instead of on prem mailbox

Let’s take a look at the checklist which would help us to stay focussed:

1. Network bandwidth
2. Deciding appropriate migration path and User Sync to Azure AD
3. setting up DNS records – Autodiscover and SPF
4. Testing with an unused domain
5. Testing migration for selected users in the actual domain
6. Outlook compatibility check
7. Backing up outlook autocomplete
8. Migrate all other users before migrating top management users

Network Bandwidth

More number of users using Teams OR high network activity due to line of business applications and services might lead to poor user experience.

Consider the peak traffic and plan accordingly. Check this calculator to identify the bandwidth requirement for most used Microsoft 365 applications.

Decide right migration path for your needs

Based on your requirements and existing exchange version, choose appropriate migration path. Click here to read Microsoft documentation about the possible migration path. Choosing the right path initially would save a lot of time.

Things to consider when choosing the path:

1. Current exchange version
2. Do you want On prem domain controllers to be primary directory?
3. Are you looking to migrate mailboxes in batches and have co-existence between Exchange online and on prem Exchange?
4. When choosing hybrid migration, do you have supported Exchange commutative update installed to get support from Microsoft?
5. If Exchange attributes are synced to Azure AD, fresh mailboxes cannot be created in Microsoft 365. It would ask to migrate mailbox first. Remove attributes from Azure AD connect if you do not want to go with Exchange Hybrid – all attributes starting with ‘msExch’. Click here to know about excluding attributes from AD Connect.

2 more tips:

PST Migration: Export PST from Exchange and import them into Exchange Online. This is one of the simple way to Migrate mailbox but needs additional configuration to be done for batch migration. Click here to know more about setting up Exchange co-existence instead of using Exchange Hybrid migration.

Email migration from Outlook: An easy way to export PST from outlook, remove existing mailbox and add newly created Microsoft365 mailbox. Import the PST back. Syncing mails would take sometime.

Setting up DNS records:

With some migration approach, there is no need to change the Autodiscover record/MX record which can be switched at the end. While others may need to change the record. Test it with an unused domain before trying it out in production.

When hybrid migration is not used, this is required most of the times. When adding Microsoft 365 mailbox to user’s outlook profile, for domain joined computers, ExcludeScpLookup registry needs to be added so that outlook client does not pick Exchange from on prem AD and internal AutoDiscover record should point to autodiscover.outlook.com.

Outlook compatibility with Microsoft 365

Outlook 2010 or any older version does not work with Exchange online hosted mailbox.

For Outlook 2013, we need to add registry key to force use of modern authentication (EnableADAL to 1).

For Outlook 2016 and newer version, no change is needed. It supports modern authentication by default.

However, ExcludeScpLookup key would need to be added for Outlook 2013 and Outlook 2016 to skip AD SCP lookup.

If you do not receive modern authentication prompt when configuring outlook, make sure that Modern Authentication is enabled for the tenant and run fiddler to check what’s happening behind the scenes. Click here to learn about outlook autodiscover.

Outlook Autocomplete

This is a feature in outlook which helps in autocompleting email addresses if an email is sent to the recipient earlier. This information is stored in the mailbox. When a new Microsoft 365 mailbox is configured in outlook, it would not have the old autocomplete addresses.

Click here for the most easiest way to backup and restore the autocomplete file from one mailbox to other.

I hope this helped. Good luck for your migration journey. If you have any questions, please drop a comment below or get in touch with me. I would be glad to help.