need use another emails for additional tiers?

2016509

for example - If I use this scheme (6 tiers) - I need to have 10 emails for each project.

Those. Do I have to have 60 different emails?

Hinkys

As long as you're targeting different sites across all tiers, you can use just 1 email. You need multiple emails only if you plan on building multiple accounts on the same sites. (and / or if they get banned - not too sure how's the situation with that these days)

So in theory, if you're using the same verified list for each tier and you're only doing 1 account per site in each tier, you can use 5 emails (1 per project).

This is all assuming you're talking about disposable emails, not catchalls.

But to really answer your question, 60 (10 per project) is an arbitrary number. The more you have, the more links you can build without having to touch any project, replace emails or verified list, etc.