I'm going to use examples to try to explain the dilemma I'm in.

My client has an organization that was created with their gmail account for example: example@gmail.com

My client website is https://example.com

I want my client to invite me into their organization, so im thinking of creating an email account called: webmaster@example.com that I would have access to(as their developer) and that they can invite into the organization.

The thing is, what would happen in the future if I decide to connect their example.com domain to the organization? Especially if they want to move their current custom email service to Zoho Mail? 

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I'm asking this because I first told them to invite my email to their Zeptomail account as an "Engineer" so that I can set it up for them, but when I tried to accept the email, it said I was already part of an organization (my own, since I use Zoho as well) so I couldn't accept the invite.

So I'm wondering what would happen in the future if I decide to bring their email or other services to Zoho and decide to attach it to their domain example.com and then start creating email accounts like info@example.com from within Zoho.

Would the webmaster@example.com email that was invited into Zeptomail still be able to access Zeptomail?