I'm having trouble migrating my e-mails into Zoho Mail.

Previously I had a web hosting account with a 3rd party which allowed me to host multiple sites. One of these sites was the domain I'm now using with Zoho Mail but it never had a website, just mailboxes in Cpanel.

In order to set-up my account with Zoho Mail I first had to change the nameservers of my domain back to my domain registrar (GoDaddy) so that I could then update the DNS records for Zoho Mail.

After I added my users to Zoho Mail I then started to migrate my mailboxes via IMAP. The first migrated perfectly. However at that stage it looks like the domain change hadn't fully propagated as the mailbox in cpanel was still saying that the mail server was mail.mydomain.com. When I came to migrate the other mailboxes, I noticed that the mail servers had changed back to that of my web host ukm11.siteground.biz. I created a new migration using these details but whilst no error is generated, it never gets past 0% complete and no e-mails are imported.

I can't figure out what I'm doing wrong when the first one worked. Is it just that the DNS changes haven't fully propagated and if I try again tomorrow it may work?