I recently moved my custom domain email from Microsoft 365 (with GoDaddy registrar and DNS) to iCloud+ (using CloudFlare as registrar and DNS). I was looking to transfer since Microsoft is going to stop officially supporting custom domain email hosting.
I simply used an email client that supports IMAP to transfer everything. Logged into the Microsoft 365 instance of the email account and had the client download ALL of the email messages. Then transferred my DNS and domain from GoDaddy to CloudFlare. Set up the custom domain email through iCloud+, set up iCloud email via IMAP in the email client, then within the email client I dragged and dropped the emails to the new account. It took over a day to transfer around 100k emails.
I recently moved my custom domain email from Microsoft 365 (with GoDaddy registrar and DNS) to iCloud+ (using CloudFlare as registrar and DNS). I was looking to transfer since Microsoft is going to stop officially supporting custom domain email hosting.
I simply used an email client that supports IMAP to transfer everything. Logged into the Microsoft 365 instance of the email account and had the client download ALL of the email messages. Then transferred my DNS and domain from GoDaddy to CloudFlare. Set up the custom domain email through iCloud+, set up iCloud email via IMAP in the email client, then within the email client I dragged and dropped the emails to the new account. It took over a day to transfer around 100k emails.