How to test the layout of email newsletters?

Question

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There is a layout for email newsletters, you need to test how it works in email clients. How can this be done?
(I haven't experienced this before)

Answer 1

https://litmus.com/ or https://www.emailonacid.com/ .
To check Russian mailers, you will have to send test letters to them

Answer 2

For sending to domestic mailers, I used mozilla thunderbird. I immediately sent it en masse to all my test boxes and looked.