Service Desk - forward email from Zoho

Hello, I have configured Zoho mail with my custom domain like
I want to use the GitLab Service Desk feature on but I won’t force my users to use GitLab mail addresses like
So I thought I can set up my Zoho mail email forwarding. Then my users can use a more friendly address.

My problem is when I want to add Gitlab email to Zoho I have to do the verification. On GitLab, I received confirmation mail as an issue but the verification email doesn’t contain any content.
Does GitLab have restrictions for the email body?