I've completed the migration of all production and shared mailboxes from our on-premises Exchange 2016 to Exchange Online. Currently, emails are still flowing from the on-prem setup to Exchange Online or through our Sophos outbound filter. I've verified DMARC, SPF, and DKIM keys for Exchange Online. All email users in Active Directory are part of a "365 Sync" group that syncs with Microsoft 365. Is there anything else I should do before switching the DNS to point to Exchange Online and updating Autodiscover settings both internally and externally? The on-prem server will remain operational for now, but I want all email traffic to go through Exchange Online.
3 Answers
Before making the switch, consider lowering the TTL on your public DNS records. This way, if you need to reverse the change, it'll be quicker to revert. High TTLs can create real issues if you encounter problems later on.
Great tip! I’ll reduce mine from 3600 to 600.
I just finished a similar migration. Make sure to install the necessary Exchange tools and follow Microsoft’s best practices. You might want to set up something like Postfix for mail flow from the on-prem to 365.
I’m taking on a similar project and found this blog that has been super helpful: alitajran.com/exchange-hybrid. It goes in-depth on everything you need to know for the migration.
Absolutely! I've seen clients get stuck with MX records set to a two-week TTL, which caused a ton of headaches.